Fix #141 "Loader::raster_bounds" to work as intended.

[ikatson]

This fixes issue #141, so that Loader::raster_bounds actually returns tight raster bounds.
Previously, it returned distorted bounds due to usage of "RectF::set_origin_y"
which does not preserve Rect size.

[jrmuizel]

Can you add a test as well?

[ikatson]

@jrmuizel I can surely try my best, can you please recommend what's an appropriate test for this use case?
For example, I could test that size of the rect with size 1.0 is comparable to the size of typographic_bounds(), but that would not test the actual origin.
Or I could just hard-code some expected raster_bounds for a sample glyph from a sample font - but then which font should I use?
Also this method is on the trait, but it's not used on Windows, so how should I go about testing on other platforms? (I only have a mac)
Thanks

[jrmuizel]

You can probably just hard code the expected bounds for a sample glyph of Inconsolata or EBGaramond12 which are already in the repository. The existing tests in src/test.rs make use of them and you should be able to just do something similar.

[ikatson]

@jrmuizel ready for review

[ikatson]

@jrmuizel @pcwalton just checking if there's anything I need to update here for this to be good enough to merge