tmux: use fish as default command by default

On some systems it is easier to leave the user's default shell alone and
just tell tmux to explicitly start fish. When fish isn't installed, fall
back to whatever $SHELL is set to.
nvim: only show diagnostics virtual text for current line
nvim: use flake8 linter for Python
nvim: rewrite async grep using libuv

use libuv directly rather than going through the jobstart() API which
ends up going through libuv anyway.
nvim: add default tag mappings

These are overriden in buffers with an LSP server, but they act as a
good fallback.
nvim: phase out Fugitive autocommand

According to the fugitive docs, the Fugitive User autocommand is being
phased out in favor of just checking the result of FugitiveGitDir() on a
BufRead/BufNewFile autocmd.
nvim: set LSP diagnostic colors in colorscheme
weechat: update to 3.2
nvim: fix server configuration

To use a variable as a key in a Lua table, you have to surround it with
brackets; otherwise, it's interpreted as a literal string.
nvim: make fugitive work for dotfiles

This requires manually setting b:git_dir and modifying the git wrapper
to still set '--git-dir' with '-C $HOME' as an argument.
nvim: fix ifndef snippet
nvim: gitsigns: defer loading until fugitive is enabled

Also use the b:gitsigns_head variable in the statusline, if available.
nvim: disable Telescope tags

It doesn't check the &tags option so it can't find the tags file created
by Gutentags.
nvim: use snippets.nvim
nvim: replace ale with nvim-lint
nvim: set cursorline autocmds in init.vim
nvim: move packer to plugin/ directory
nvim: fix typo in VimEnter autocmd
nvim: lazy load nvim-compe
fish: prefer doas if installed