Add an option to display total line number in the location component

[thisisrandy]

Adds total_lines_in_location option to display location as current_line/total_lines:current_col. Two notes:

1. I modeled location.lua off of fileformat.lua in order to have access to self.options. This may not be the best approach.
2. This PR is INCOMPLETE. In particular, it doesn't include docs updates. There might reasonably be a test to write, too. Haven't explored that yet. The motivation for the current PR is to see if the maintainers approve of the approach and solicit any comments.

[thisisrandy]

Addresses #1333

[thisisrandy]

I'm trying to test locally and running into some issues. What exactly is meant (from CONTRIBUTING.md) by "For running tests you'll have to make sure lualine.nvim, plenary.nvim and nvim-web-devicons are in same directory"? The expected directory tree would be helpful.

I interpretted this as, "copy the contents of the plenary/icons lua and scripts dirs into the same dirs in your lualine dir," and that got me through linting without any errors. However, make test unhelpfully outputs the following and then immediately exits with 0:

nvim --headless --noplugin -u scripts/minimal.vim -c "PlenaryBustedDirectory tests/plenary/ {minimal_init = 'tests/minimal_init.vim', sequential = true}"
Starting...%