Fix origin transform in DrawInternal with src rect

This change fixes a transform applied on the origin parameter
passed to DrawInternal, based on the ratio between the destination
rectangle and the texture width / height.

When a source rectangle has been specified, its size should be used
instead.
Fix edge-case when source rect has 0 width/height

Nothing would get rendered when the source rectangle had a width or
height of zero, whereas XNA does render something.
Added comments to Color
Color fix
Color comment fixes
#1244 Transparent versions of the logo graphics and icons.
#1245 Icons and graphics for use on a dark background.
updated comment regarding the missing 32x32 and 48x48 sizes for the dark background graphics.
Merge pull request #1174 from elisee/fix_spritebatch_draw_origin

Fix origin transform in DrawInternal with src rect
Merge pull request #1302 from Shqrdx/test

Added comments to Color
Updated Readme.MD as requested in #1143.
Added jenkins build status image to header.
Tiny update.
Tiny typo fix.
Updated headings capital casing so they are consistent.
Merge pull request #1312 from raistlinthewiz/readme-md-update

Updated Readme.MD as requested in #1143.
Merge pull request #1308 from SickheadGames/TitleContainer

TitleContainer Fixes
Updated API docs for TouchCollection.cs.
Merge pull request #1307 from totallyeviljake/ISSUE_1245_R1

Issue 1245 Graphics For A Dark Background
Merge pull request #1306 from totallyeviljake/ISSUE_1244_R1

#1244 Transparent versions of the logo graphics and icons.