Clevercsv

* Update URL regex to avoid catastrophic backtracking and increase
performance. See [issue
13](https://github.com/alan-turing-institute/CleverCSV/issues/13) and
[issue 15](https://github.com/alan-turing-institute/CleverCSV/issues/15).
Thanks to kaskawu for the fix and jlumbroso for re-raising the issue.
* Add ``num_chars`` keyword argument to ``read_as_dicts`` and ``csv2df``
wrappers.
* Improve documentation w.r.t. handling large files. Thanks to jlumbroso for
raising this issue.

* Add an ``explore`` command to the command line application for CleverCSV.
This command makes it easy to start exploring a CSV file using the Python
interactive shell.

* Split the package into a "core" and "full" version. This allows users who
only need the improved dialect detection functionality to download a version
with a smaller footprint. Fixes [issue
10](https://github.com/alan-turing-institute/CleverCSV/issues/10)]. Thanks
to seperman.

* Fix speed of ``unix_path`` regex used in type detection. ([issue
13](https://github.com/alan-turing-institute/CleverCSV/issues/13)). Thanks
to kaskawu.

* Add ``stream_csv`` wrapper that returns a generator over rows
* Minor update to the URL type detection
* Documentation updates

* Fix bugs discovered from fuzz testing ([issue
7](https://github.com/alan-turing-institute/CleverCSV/issues/7))
* Minor changes to readme and code quality