Performance: improve type-stability of optimize_ticks
Improve type-stability of apply_scale
Improve type-stability of apply_statistic
Improve type-stability of apply_coordinate
Merge branch 'pull-request/11577830' of https://github.com/timholy/gadfly into timholy-optimization

Conflicts:
	src/statistics.jl
	src/ticks.jl
Make @timholy's optimization work with non-Real types.
Fix some inconsistencies between plot(...) and plot(layer(...)). Fixes #336
Improvements to histogram bin count selection. See #343
Correct labels on sqrt scales. Fixes #299
Start keeping track of significant changes in NEWS.md
Fix "no method" error in issue 293
Fix contour line ordering issue from #293
Merge pull request #350 from darwindarak/contour_preserve_order

Fix contour line ordering issue from #293
Improvements to histograms in subplots.
Fix bincount being ignored in some histograms. Fixes #351
Adapt to Iterators changes.
Reimplement toggleable color keys. Fixes #353.
Shift-clicking key will toggle all but the clicked entry. See #353
Test against Compose master.
Re-export PGF from Compose.