Selecting items from a list with tlib's tlib#input#List() function

tlib#input#List() lets users select one are many items from a list. In
this demonstration, we select two files from a list of about 500
filenames.

We use the :Tragfile command, which is sets the initial filter to
"parts" of the current file's basename. The current document is called
"post_tlib.txt". Since no file matches "post_tlib", the initial list is
empty. We remove that filter to see the whole list by typing <C-BS>.

    1. Find: Filter_cnf.vim (from tlib_vim)
       Type: Fi cnf.<CR>
       Or:   Fi<ALT-4>
    2. Find: vikitasks.vim (from vikitasks_vim)
       Type: vikit<CR>
       Or:   task<ALT-2>

Besides the "cnf" filter used in this demonstration, tlib also supports
fuzzy matching (as seen on TV).