1. Add ale.setup and ale.setup.buffer for pure Lua configuration.
2. Update many global settings to use Booleans instead of numbers to
make types easiert to work with in Lua.
3. Radically reformat documentation and fix errors to make
documentation more usable for Neovim users.
Like many other linters, use variables for the executable and options
used by the linter.
By default, the linter now report every warnings as errors with
`--warning-errors`.
Also add include directory and set working directory to file directory.