Add missing parentheses and whatnot, move dangling comment, etc. Some
specific items worth mentioning:
Fixed some references to non-existent tags, found via `make html`
msgpack_rpc/channel.c:
ELOG already prefixes each line with "error @ ..."
* "Python" is a proper noun and should be capitalized in prose
* Corrected use of "its/it's"
* Used better preposition to describe something "in" legacy Vim
* Combine fragments into complete sentence
- Improved wording in a few places for clarity
- Various capitalization/grammar fixes
- Change references to Neovim as 'editor' to 'Nvim'
- Be consistent regarding utilization of vim's documentation features,
e.g. unnamedclip -> |unnamedclip|
- Reflowed all changed paragraphs accordingly
- Add spaces before parentheses
- Remove trailing whitespace
- Standardize single spaces after periods. Vim's docs use two for the
most part, but Nvim's use one mainly, so just follow Nvim's conventions
