0.7.0

• GlyphCalculator allows font calculations / pixel bounds etc without actually being able to draw anything, or the need for gfx objects. Using a scoped caching system.
• Update to rusttype 0.3.0
• Cache / font lifetime changes made to rusttype allow removing the .standalone() calls when adding glyphs to the gpu-cache. This and other rusttype optimisations can result in up to ~25% faster worst case performance (worst case being no position/draw caching / text changes every frame).
• OwnedVariedSection & OwnedSectionText to help some edge cases where borrowing is annoying.
• Simple Debug implementations to allow end users to derive more easily.