Support l() function name in Extract::Plugin::Perl.

Hi Clint,

This is the first of three pull request regarding adding HAML support to Locale::Maketext::Lexicon. It adds the name "l" as a valid translation function to E::P::Perl and E::P::PPI. This is to done mainly to support the fact that the Mojolicious MVC framework imports this function into its templates, both the default EP ones and HAML ones, if you choose to use HAML.

In the next pull request, the next E::P::Haml plugin will make use of this functionality.

Regards,
Calum