Document template filters (closes #4)

Author: TkTech

docs/index.rst

@@ -91,6 +91,25 @@ Example selector functions::
 The example above assumes that the current user is stored on the
 :data:`flask.g` object.
 
+Jinja Filters
+-------------
+
+Several commonly used formatters are added as jinja template filters after
+calling `init_app().` For dates and times, these are:
+
+- `<datetime>|datetimeformat` -> `format_datetime`
+- `<date>|dateformat` -> `format_date`
+- `<time>|timeformat` -> `format_time`
+- `<timedelta>|timedeltaformat` -> `format_timedelta`
+
+And for numbers, these are:
+
+- `<number>|numberformat` -> `format_number`
+- `<number>|decimalformat` -> `format_decimal`
+- `<number>|currencyformat` -> `format_currency`
+- `<number>|percentformat` -> `format_percent`
+- `<number>|scientificformat` -> `format_scientific`
+
 Formatting Dates
 ----------------