Have BaseAxis take in `any` as the formatter arg.
If it receives a function, then it wraps it in a CustomFormatter
CustomFormatter is set properly if generated thru the Axis.formatter
Merge pull request #679 from palantir/cat-axis-formatter-2

Have BaseAxis take in `any` as the formatter arg.
Actually remove axis.ts file.
Merge branch 'master' into HEAD

Conflicts:
	plottable.d.ts
Merge pull request #686 from palantir/customFormatter-api

Custom formatter api
Merge pull request #688 from palantir/remove-axis-ts

Actually remove axis.ts file.
Release version 0.20.1
Fix type signature on NumericAxis.ts
Release version 0.20.2
Make Abstract.Axis.formatter into a getter/setter
Version 0.20.3
Merge tag 'v0.20.3' into 674-bar-hover-label