perf: use `vim.api.nvim_set_hl()` for speed

As noted in this thread:

- https://www.reddit.com/r/neovim/comments/sihuq7/psa_now_you_can_set_global_highlight_groups_ie/

we can expect this to be faster. On this machine (mid-2015 15" MacBook
Pro), our `nvim --startuptime vim.log` goes from:

    145.776  000.750  000.146: sourcing /Users/wincent/.config/nvim/pack/bundle/opt/cmp-buffer/after/plugin/cmp_buffer.lua
    151.221  001.641  001.641: sourcing /Users/wincent/.config/nvim/pack/bundle/opt/base16-nvim/colors/base16-bright.lua
    151.785  000.361  000.361: require('indent_blankline.utils')

to:

    140.661  000.604  000.079: sourcing /Users/wincent/.config/nvim/pack/bundle/opt/cmp-buffer/after/plugin/cmp_buffer.lua
    144.820  001.082  001.082: sourcing /Users/wincent/.config/nvim/pack/bundle/opt/base16-nvim/colors/base16-bright.lua
    145.383  000.314  000.314: require('indent_blankline.utils')

Columns are:

    clock   self+sourced   self:  sourced script

So, incredibly scientific results are that we dropped from 1.641ms to
1.082ms with this change. In practice, however, I always find that the
gap between the previous file's clock and the file of interest's clock
tells the full story: if we use that metric, we went from 151.221ms -
145.776ms (ie. 5.445ms) to 144.280ms - 140.661ms (ie. 3.619ms). ie.
there is some unaccounted for time in the "self" metric that probably
corresponds to reading the file and parsing it. Either way, this is a
small win but a gratefully accepted one.

docs: fix grammar

docs: add notes on how to update

Because it is complicated enough, and infrequent enough, that I could
easily forget a path, or to do a step.

feat: add support for special names (NONE, bg, etc)

This backports:

- https://github.com/chriskempson/base16-vim/commit/c8a7da6f5fa890a621d4fec11ef09c9b3559f32a

From:

- https://github.com/chriskempson/base16-vim/pull/217

How I did this:

1. Made changes to the template in the submodule in my dotfiles repo (at
   `aspects/nvim/files/.config/nvim/pack/bundle/opt/base16-nvim`).
2. Copied them up to the superproject working area with:
   `cp aspects/nvim/files/.config/nvim/pack/bundle/opt/base16-nvim/templates/default.mustache
   vendor/base16-templates/base16-nvim/templates`.
3. Ran `NO_CLONE=1 support/base16-builder.rb`.

feat: tweak Statement color

This backports:

- https://github.com/chriskempson/base16-vim/commit/06cc5591498c88200e58c97b67cf3913db0f5af1

From:

- https://github.com/chriskempson/base16-vim/pull/210

How I did this:

1. Made changes to the template in the submodule in my dotfiles repo (at
   `aspects/nvim/files/.config/nvim/pack/bundle/opt/base16-nvim`).
2. Copied them up to the superproject working area with:
   `cp aspects/nvim/files/.config/nvim/pack/bundle/opt/base16-nvim/templates/default.mustache
   vendor/base16-templates/base16-nvim/templates`.
3. Ran `NO_CLONE=1 support/base16-builder.rb`.

feat: add LSP highlight groups

This backports:

- https://github.com/chriskempson/base16-vim/commit/db92479478ebccbb2c11874e4b730477653414a5

From:

- https://github.com/chriskempson/base16-vim/pull/222

How I did this:

1. Made changes to the template in the submodule in my dotfiles repo (at
   `aspects/nvim/files/.config/nvim/pack/bundle/opt/base16-nvim`).
2. Copied them up to the superproject working area with:
   `cp aspects/nvim/files/.config/nvim/pack/bundle/opt/base16-nvim/templates/default.mustache
   vendor/base16-templates/base16-nvim/templates`.
3. Ran `NO_CLONE=1 support/base16-builder.rb`.

chore: update with new schemes

4 new schemes:

- base16-danqing-light
- base16-gruber
- base16-vice
- base16-vice-alt

And 1 scheme with very minor tweaks:

- base16-tender

Generated this by running `support/base16-builder.rb` from my dotfiles:

- https://github.com/wincent/wincent/blob/main/support/base16-builder.rb

Then committing the results.

chore: add .mailmap file

chore: replace bad links

These all point at some kind of crypto/casino site now (I can't bear to
even read it closely enough to know _what_ it is), so replace them with
a non-radioactive link instead.

fix: adjust template to match what was actually used to generate outputs

chore: initial import

Extracted from my dotfiles:

    https://github.com/wincent/wincent/tree/63ae5ac88edac5ab877737bd964af09983ea1bc6/vendor/base16-templates/base16-nvim

This is a port to Lua of base16-vim:

    https://github.com/chriskempson/base16-vim

As this is a heavily derivative work, I've preserved the original
copyright notice in the LICENSE.md.