Add locale support for decimal separator in intword

[hugovk]

Fixes #93.

import humanize
_t = humanize.i18n.activate("it_IT")
print(humanize.thousands_separator())
print(humanize.decimal_separator())
print(humanize.intcomma(1234559.123))
print(humanize.intword(1234559.123))

Before:

.
,
1.234.559,123
1,2 milioni

After:

.
,
1.234.559,123
1.2 milioni

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.51%. Comparing base (3dca143) to head (7175184).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #287   +/-   ##
=======================================
  Coverage   99.51%   99.51%           
=======================================
  Files          11       11           
  Lines         829      831    +2     
=======================================
+ Hits          825      827    +2     
  Misses          4        4           

Flag	Coverage Δ
macos-latest	97.83% <100.00%> (+<0.01%)	⬆️
ubuntu-latest	97.83% <100.00%> (+<0.01%)	⬆️
windows-latest	95.90% <100.00%> (+<0.01%)	⬆️

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