Add rudimentary template support for the menu entries

This patch introduces 3 new configuration variables:

    g:qcc_format_word (default: "${0} <${1}>")
    g:qcc_format_abbr (default: "${0}")
    g:qcc_format_menu (default: "${2}")

Which are used to generate the complete menu entries (read the help
for 'complete-items' for more details on the meanings of each)

The default format is the original one.

Given an output (from running g:qcc_query_command) like:

FirstName LastName<TAB>email@domain.com<TAB>details

The generated completion menu would look like:

    FirstName LastName | details

And selecting the entry completes it to:

    FirstName LastName <email@domain.com>