- Remove unused variables.
- Do not use helpers.nvim_feed in most cases.
- Do not use helpers.nvim and helpers.nvim_eval at all.
- Add helpers.funcs and helpers.\*meths special tables. Indexing such table 
  creates functions which call helpers.call or helpers.nvim (and similar) with 
  first argument equal to table index.

What works:

1. ShaDa file dumping: header, registers, jump list, history, search patterns,
   substitute strings, variables.
2. ShaDa file reading: registers, global marks, variables.

Most was not tested.

TODO:

1. Merging.
2. Reading history, local marks, jump and buffer lists.
3. Documentation update.
4. Converting some data from &encoding.
5. Safer variant of dumping viminfo (dump to temporary file then rename).
6. Removing old viminfo code (currently masked with `#if 0` in a ShaDa file for
   reference).