docs: categorize Language Definition functions

- multi-type / misc functions
- Type Conversion functions
- String functions
- Date functions
- Number functions
- Array functions
- Map functions

- also consistently use `str`, `array`, `n`, `v` for the variable name when referring to a specific type
  - `array` was used consistently for older functions, but not some newer ones
  - `str` added to match `array`
  - `n` was sometimes used for numbers or ints, but not always
  - `v` is for multi-type "values"

Signed-off-by: Anton Gilgur <[email protected]>