Moving floating point WIP to a new branch.
Merge branch 'master' into floating-point

Conflicts:
	ast.mli
	calc.ml
	parser.mly
Fixed problem with previous merge.
Allow ints and floats to be used in the same expr.

There is the one issue that ints are always coerced into floats, but at least
such expressions parse now.
Added full support for floating point arithmetic.