Atlas builder Ant Task with improvements

Hi, this pull request adds an Ant Task for the Atlas Builder with the following features ;
- Ant Task
- define sprites from a bigger images (i.e. one source file can contain more than one sprite) with different resolution support (i.e. scaling coordinates),
- include font in atlas
- extends font with custom sprite
- specify hot points for sprites
- use different padding for sprites of the same atlas
- use custom filtering durring generation (for hover effect, preparing for linear filtering,...)
- merging of last pages of differents packs

Here is an example of an ant file using it ;

```XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<project name="explorers-assets" basedir="." default="assets">
	<taskdef name="buildatlas" classname="com.badlogic.gdx.tools.imagepacker.AtlasBuilderTask" />

	<typedef name="glowFilter" classname="com.jhlabs.image.GlowFilter" />
	<typedef name="bleedFilter" classname="com.badlogic.gdx.tools.imagepacker.BleedToTransparentFilter" />

	<target name="makeAtlas" depends="checkforAtlaschanges" unless="atlas.nochanges">
		<buildatlas dst="${assets-out}" name="explorers">
			<img ref="ui-elements" src="${assets-gen}\atlas-ui.png" />
			<img ref="map-elements" scale="2" src="${assets-gen}\atlas-map.png" />
			<img ref="portrait-thief-male" src="${assets-src}\Zeldyn - CC-BY - Portraits\theifportmale.png" />

			<effect name="icon">
				<image suffix="-up" />
				<image suffix="-over">
					<glowFilter amount="0.25f" radius="1.0f" />
				</image>
				<image suffix="-down">
					<glowFilter amount="-0.075f" radius="1.0f" />
				</image>
			</effect>
			
			<effect name="zoomable">
				<image>
					<bleedFilter alphaThreshold="32" />
				</image>
			</effect>

			<settings maxWidth="2048" maxHeight="2048" rotation="false" fast="true" />

			<mergepack name="ui-pack" packs="fonts, ui" />
			<mergepack name="main" packs="map, ui-pack" />

			<pack name="fonts">
				<settings paddingX="0" paddingY="0" stripWhitespaceX="true" stripWhitespaceY="true" ignoreBlankImages="false" filterMin="Nearest" filterMag="Nearest" />
				<font ref="black-chancery-70" src="${assets-src}\BlackChancery.fnt" />
				<font ref="font-17" src="${assets-src}\skin\default.fnt">
					<extraChar char="167" ref="star" xAdvance="32" />
					<extraChar char="168" ref="star-darken" xAdvance="32" />
					<extraChar char="163" ref="arrow" xAdvance="32" />
				</font>
				<sprite from="ui-elements" ref="star" x="416" y="0" w="32" h="32" hoty="6" />
				<sprite from="ui-elements" ref="star-darken" x="416" y="192" w="32" h="32" hoty="6" />
				<sprite from="ui-elements" ref="arrow" x="416" y="32" w="32" h="32" hoty="6" />
			</pack>

			<pack name="ui">
				<settings paddingX="0" paddingY="0" stripWhitespaceX="true" stripWhitespaceY="true" ignoreBlankImages="false" filterMin="Nearest" filterMag="Nearest" />
				<sprite img="${assets-src}\texture\particle-cloud.png" ref="particle-cloud" />
				<sprite img="${assets-src}\texture\particle-star.png" ref="particle-star" />
				<sprite img="${assets-src}\texture\particle-fire.png" ref="particle-fire" />
				<sprite img="${assets-src}\texture\particle.png" ref="particle-dot" />

				<sprite from="portrait-thief-male" ref="portrait-thief-male-05" fitx="53" fity="70" />
				<sprite from="portrait-thief-male" ref="portrait-thief-male-04" fitx="42" fity="56" />
				<sprite from="portrait-thief-male" ref="portrait-thief-male" fitx="96" fity="128" />

				<sprite from="ui-elements" ref="lightning-gradient" x="65" y="80" w="1" h="25" />
				<sprite from="ui-elements" ref="date-roll" x="64" y="80" w="1" h="25" />
				<sprite from="ui-elements" ref="month-roll" x="752" y="432" w="36" h="208" />
				<sprite from="ui-elements" ref="day-roll" x="787" y="432" w="16" h="176" />
				<sprite from="ui-elements" ref="month-3-roll" x="800" y="432" w="16" h="80" />
				<sprite from="ui-elements" ref="month-2-roll" x="800" y="496" w="16" h="64" />
				<sprite from="ui-elements" ref="white-back.9" x="48" y="96" w="16" h="16" />
				<sprite from="ui-elements" ref="cursor.9" x="48" y="80" w="5" h="5" />
				<sprite from="ui-elements" ref="icon-back" x="832" y="192" w="48" h="48" effects="icon" />
				<sprite from="ui-elements" ref="icon-exit" x="880" y="192" w="48" h="48" effects="icon" />
				<sprite from="ui-elements" ref="icon-trophy" x="512" y="304" w="64" h="64" effects="icon" />
				<sprite from="ui-elements" ref="icon-upgrade-panel" x="576" y="304" w="64" h="64" effects="icon" />
			</pack>

			<pack name="map">
				<settings paddingX="16" paddingY="16" stripWhitespaceX="true" stripWhitespaceY="true" ignoreBlankImages="false" filterMin="MipMapLinearNearest" filterMag="Linear" />
				<sprite from="map-elements" ref="buildings-dock-1" x="736" y="96" w="48" h="48" />
				<sprite from="map-elements" ref="buildings-dock-2" x="784" y="96" w="48" h="48" />
				<sprite from="map-elements" ref="buildings-dock-3" x="832" y="96" w="48" h="48" />
				<sprite from="map-elements" ref="buildings-dock-4" x="880" y="96" w="48" h="48" />
				<sprite from="map-elements" ref="buildings-dock-5" x="928" y="96" w="48" h="48" />
				<sprite from="map-elements" ref="buildings-dock-6" x="976" y="96" w="48" h="48" />
				<sprite from="map-elements" ref="tiles-pasture" x="0" y="896" w="128" h="128" effects="zoomable" />
				<sprite from="map-elements" ref="tiles-forest" x="128" y="896" w="128" h="128" effects="zoomable" />
				<sprite from="map-elements" ref="tiles-sea" x="256" y="896" w="128" h="128" effects="zoomable" />
				<sprite from="map-elements" ref="icon-upgrade" x="544" y="48" w="48" h="48" hotx="22" hoty="22" effects="icon" />
				<sprite from="map-elements" ref="icon-downgrade" x="832" y="48" w="48" h="48" hotx="22" hoty="22" effects="icon" />
			</pack>

		</buildatlas>
	</target>

</project>```