FlxTilemap ignores last tiles if startingIndex is > 0

_tileObjects now takes startingIndex into account.

Fixed FlixelCommunity/flixel#55, AdamAtomic/flixel#176
overlapProcessed isn't properly cleared in FlxQuadTree

_notifyCallback is now only called is _processingCallback returned true that iteration.

Fixed FlixelCommunity/flixel#29, AdamAtomic/flixel#203
FlxTilemap not clearing variables before loadMap

I've added a clearTilemap function that properly resets everything before every call to loadMap. I also set visible and active to false in the constructor, so that flixel doesn't attempt to draw a tilemap before it's been loaded.

Fixed FlixelCommunity/flixel#46, AdamAtomic/flixel#185
Fixed FlixelCommunity/flixel#34, AdamAtomic/flixel#197
Fix FlxObject#(overlaps|overlapsAt) checking only first element of FlxGroup

FlxObject#overlaps and FlxObject#overlapsAt had a bug that would lead to only the first element of a FlxGroup being checked. It was happening because the variable "length" was not locally declared, however there was no compiling warns/errors because the Object class has a property named "length".
Add `FlxGroup::revive()`

The FlxGroup will now revive itself, and then all its members.

This is to compliment `FlxGroup::kill()`.
Tweaks for FlxObject.overlap* and fixes for FlxTilemap.overlap*

I extended the fixes of FlxObject.overlap*() to FlxTilemap.overlap*(). I also added a break statement when a collision is detected since all overlap() methods return just a boolean.

Fix https://github.com/FlixelCommunity/flixel/issues/39 and https://github.com/AdamAtomic/flixel/issues/192 .
Small code refactoring.
Fix minor typos in `FlxGroup::revive()`

It's a minor typo, but with major consequences!

If left unchecked, this bug would revive already existing objects,
leading to several Science Fiction worthy paradoxes.

Also fixed a tiny spelling typo in the ASDoc.
Only revive `FlxGroup` objects if they are `alive`

After some discussion on GitHub
https://github.com/FlixelCommunity/flixel/pull/110/files#r1831839
it seems the more logical to check if an object is `alive`,
rather than check if it `exists` when reviving it.
Fix `FlxCamera` jitters when following a target

Resolves the following issue:
 * https://github.com/FlixelCommunity/flixel/issues/5 - https://github.com/AdamAtomic/flixel/issues/227

Fix provided by [Krix](https://github.com/krix)
Rename `FlxSprite::simpleRender` to `isSimpleRender`

Will also avoid an error if the `target` object is not a `FlxSprite`.
no need to fill a camera twice if not blending alpha
Change `FlxSprite::isSimpleRender` into a function

Also does some minor cleanup of making sure brace placement matches the rest of the code, and removes one unecessary comment.
Fix issue #37 FlxTilemap.overlapsWithCallback calls callback when no overlapping.

The overlapping check performed for tiles with allowCollision = false ignored the object widht/height, so the tile callback would fire even when the Object was placed close to, but not overlapping, the tile.
Fix regression introduced by camera fix.

Pull request 119 https://github.com/FlixelCommunity/flixel/pull/119 fixed issue #50, but it introduced a new bug related to the camera bounds. This commit reverts all changes made by pull request 119, fixing the introduced FlxCamera problems.
Merge pull request #171 from Dovyski/fix_issue_165

Fix regression introduced by camera fix.
Merge pull request #99 from moly/fix_issue_176

FlxTilemap ignores last tiles if startingIndex is > 0
Merge pull request #100 from moly/fix_issue_203

overlapProcessed isn't properly cleared in FlxQuadTree
Merge pull request #110 from IQAndreas/fix-flxgroup-kill

Add `FlxGroup::revive()`
Merge pull request #166 from Dovyski/fix_issue_37

Fix issue #37 FlxTilemap.overlapsWithCallback calls callback when no overlapping