thousands_separator and decimal_point in web.utils.commify

Old behavior: 
We can't specify decimal point or thousands separator in web.utils.commify()

New behavior:
Both decimal point and thousands separator can be optionally set.
Note:
- Default value for decimal point (decimal_point) is '.'
- Default value for thousands separator (thousands_separator) is ','

Added example:
```python
>>> commify(1234.5, decimal_point=',', thousands_separator='.')
'1.234,5'
>>> commify('%.2f' %1234.5, decimal_point=',', thousands_separator='.')
'1.234,50'        
```