Restest

- ENH: now path parser expands key values using \_expand_var before starting the search

- ADD: `NOT_NULL` and `IS_NOT_NULL` test modes (same as `EXIST`, `EXISTS` and `!!` )
- ENH: now restest throws an error if a test mode is mispelled or not existent.
- ENH: now restest shows the operation request even if it is not able to show results.

- ADD: support for comments. You can add a comment using the "rem" command, or
by putting an `` sign at the beginning of a line (**note**: using `` makes the
JSON invalid)

- ADD: now the variables inside inner structures are expanded recursively

- ENH: now action `dump` can write to console, if you pass `"print": true` attribute

- ADD: is now possible to upload multiple files with the same field name

- ADD: new --curl option to see curls on console (on stderr)
- ENH: Now GET requests can have url parameters defined in "params" instead of the URL path.
- ENH: Better CURL formatting for easier debug
- ENH: Updated documentation
- FIX: error accessing not existing tokens in tests
- FIX: better error handling for out of bounds list index

- brand new path parser that enanches the search of keys inside nested structures