Issue #5988: Delete deprecated functions PyOS_ascii_formatd, PyOS_ascii_strtod, and PyOS_ascii_atof.

pystrtod.c, floatobject.c and dtoa.c.

PyOS_double_to_string, and deprecate PyOS_ascii_strtod and PyOS_ascii_atof.

If anyone wants to clean up the documentation, feel free. It's my first documentation foray, and it's not that great.

Will port to py3k with a different strategy.

int, long, and float __format__(), and it keeps their implementation
in sync with py3k.

Also added PyOS_double_to_string. This is the "fallback" version
that's also available in trunk, and should be kept in sync with that
code. I'll add an issue to document PyOS_double_to_string in the C
API.

There are many internal cleanups. Externally visible changes include:

- Implement PEP 378, Format Specifier for Thousands Separator, for
  floats, ints, and longs.

- Issue #5515: 'n' formatting for ints, longs, and floats handles
  leading zero formatting poorly.

- Issue #5772: For float.__format__, don't add a trailing ".0" if
  we're using no type code and we have an exponent.

Addresses the float -> string conversion, using David Gay's code which
was added in Mark Dickinson's checkin r71663.

Also addresses these, which are intertwined with the short repr
changes:

- Issue #5772: format(1e100, '<') produces '1e+100', not '1.0e+100'
- Issue #5515: 'n' formatting with commas no longer works poorly
    with leading zeros.
- PEP 378 Format Specifier for Thousands Separator: implemented
    for floats.

Add missing PyAPI_FUNC/PyAPI_DATA macros.