Add CR as a white space char in RX.space_in

CR is used in the IniFile lens as of EOL. To avoid concat ambig between
IniFile.store_to_eol and IniFile.eol, CR has to be added to Rx.space_in. This
change do not break any existing lens in the repository.
Add Splunk lens

Lens to parse Splunk configuration. Based on IniFile lens, with few differences:

* Accepts empty value in entry
* Entries without parent section are children of .anon node

Thanks to Tim Brigham for this contribution.

Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>