Now there is a new item type "PcItemDynamic" which takes function as
parameter.

When it comes to autocomplete at this position, the function is called,
the whole line is given to it (for example if autocompletion depend on
previous autocompleted field) and functio should return possible strings
how to continue.

Example usage:
 * listing some dynamic key-value storage
 * listing files in directory

To serve it to dynamic autocompletion functions. Previously passed line
was only following segment (which doesn't work).

…in Do function

Do function was split into doInternal with changed declaration and Do
with original declaration.