Remove --opt-tce.

It was slow and adds more code than it adds benefit. This fixes #50.
Remove references to --opt-tce from README.
Don't pass arguments of type State# a to foreign functions.

This is the first step towards removing State# stuff from generated code
entirely. Foreign functions still need to return [1, State#, realReturnValue]
and pass an extra State# parameter to any Haskell callbacks for now.
Remove old integer-simple cruft from the code generator.
Stop passing around State# a "values" entirely.

Functions that used to return (# realWorld, x #) now return (# x #) though.
Represent (# a #) by a in generated code.

This removes the last quirk of the FFI bindings; JS functions can now ignore
unboxed tuples and State# RealWorld crap as long as they don't mess around
with the internals of non-primitive types. (Which is completely unsafe and
highly discouraged anyway.)

This fixes #52.
Remove deprecated FFI quirks info from doc/js-externals.txt.
Fix minor inconsistencies in README.