intcomma returns scientific notation for large floats #431

intcomma() returns scientific notation for floats of 1e16 and above, with no commas added:

>>> humanize.intcomma(1e15)
'1,000,000,000,000,000.0'
>>> humanize.intcomma(1e16)
'1e+16'
>>> humanize.intcomma(1.5e20)
'1.5e+20'

I expected '10,000,000,000,000,000.0' and '150,000,000,000,000,000,000.0'. Passing ndigits works around it (intcomma(1e16, 0) gives '10,000,000,000,000,000').

This happens because f"{value:,}" on a float uses the same formatting as repr(), and that switches to an exponent at 1e16. Small floats hit the same thing, e.g. intcomma(0.00001) returns '1e-05'.