Remove profile decorators.

Only a single function should be decorated with @profile, as profiling
slows down the decorated functions and thus distorts the stats.
Initialization of these members should have moved to
AdobeFontMetricsParser with the parsing code
Simplify Dimension

- Split up into smaller, simpler classes
- About 15% faster rendering as __float__ does not need to be more
  complex than needed
- Drop support for some (unused) operators (__i*__)
Be more explicit about growing a Dimension to avoid confusion
Introduce DimensionUnit class

- 1*PT now produces a Dimension instead of a DimensionMultiplication
- Eliminates most of the DimensionMultiplication.__float__ calls
- Allow only right-multiplication with a DimensionUnit
Cache AdobeFontMetrics.get_glyph for another small performance boost
Caching StyledText.height also results in a small speedup
Storing glyphs-and-widths in lists seems to be considerably faster!