* explained a bit more the core_window_letterbox example

* fixed a few 'ups' moments that could lead to mild head pain and time loss

By removing the equal sign, if the 2 rects a right next to each other and not overlapping, there will be no collision detection. This is what a majority of other game libraries do and would make it easier to implement collisions for tile based games.

Changes:

 - Font structure has been redesigned, CharInfo structure contained character rectangle within font texture, it has not much sense, considering that it was an information relative to the font atlas generated and not the character itself, so character rectangles have been moved out from CharInfo to Font.
 - CharInfo included a data parameters to contain character pixel data (usually grayscale), generated on TTF font generation. It was inconsistent with other fonts types, so, now CharInfo includes directly an Image of the glyph.
 - REDESIGNED: GenImageFontAtlas(), additional recs parameter added, loaded and filled inside the function to export atlas characters rectangles, instead of silently modify the input CharInfo data.
 - REVIEWED: ImageTextEx(), funtion retrieved the font atlas image from the GPU, that was slow and problematic in several platforms. Now it uses directly the CharInfo image. Support for unicode codepoints has also been added.
 - REDESIGNED: ImageDraw(), now it includes an additional parameter, the color tint, not only it could be useful for several situations but also function signature is more consistent with similar functions.
 - ADDED: ImageFromImage() to generate a new image from a piece of another image.
 - REVIEWED: GetNextCodepoint(), renamed parameters to be more clear.

Also all examples and games that were affected by those changes have been reviewed.

Two functions have been renamed for coherence; previous naming was confusing for several users:

 - DrawPolyEx()         ---> DrawTriangleFan()
 - DrawPolyExLines() ---> DrawLineStrip()

Removed trail spaces

Also reviewed rlCheckBufferLimit()

Useful in case raylib compilation want to be automated and compilation config flags provided by command line.

By default, internal white texture was used to draw most of the shapes; some time ago, support for white font character from default internal font was added. That way, all basic drawing (shapes, text) could be performed without a texture change and in a single drawing pass.

Now, we move a step further and we allow configuring the texture (and rectangle) used to do the shapes drawing.

By comparing the edges of the rectangles relative to each other we can
determine if they intersect or not.

Note for me: Replace All is NOT your friend...

Library consistency rename... yes, I know, it breaks the API...

Replaced by fabs() that seem to work ok

- Some examples tweaks
- Reviewed ImageFormat()
- Use float for text fontSize

Also added new compilation FLAGS for that pourpose