Close #2281 - Separate cwd commands from commands

Working directories are now set seperately from the commands so they
can later be swapped out when running linters over projects is
supported, and also better support filename mapping for running linters
on other machines in future.

ale_linters/php/phpcs.vim

@@ -13,8 +13,7 @@ function! ale_linters#php#phpcs#GetCommand(buffer) abort
     \   ? '--standard=' . ale#Escape(l:standard)
     \   : ''
 
-    return ale#path#BufferCdString(a:buffer)
-    \   . '%e -s --report=emacs --stdin-path=%s'
+    return '%e -s --report=emacs --stdin-path=%s'
     \   . ale#Pad(l:standard_option)
     \   . ale#Pad(ale#Var(a:buffer, 'php_phpcs_options'))
 endfunction
@@ -49,6 +48,7 @@ call ale#linter#Define('php', {
 \       'vendor/bin/phpcs',
 \       'phpcs'
 \   ])},
+\   'cwd': '%s:h',
 \   'command': function('ale_linters#php#phpcs#GetCommand'),
 \   'callback': 'ale_linters#php#phpcs#Handle',
 \})