slice

The slice filter returns a substring, starting at the specified index.
An optional second parameter can be passed to specify the length of the
substring. If no second parameter is given, a substring of one
character will be returned.

If the passed index is negative, it is counted from the end of the
string.
Merge pull request #73 from joeldrapper/slice

slice
strip

Added string strip filters

- lstrip
- rstrip
- strip
Merge pull request #74 from joeldrapper/strip

strip