Revert "Support hdevtools options per buffer"

This reverts commit 4d2acd37d4c3a507486aaeece1c3a40d85d8b394.

Buffer local options don't harmonize very well with other
vim plugins like syntastic, which looks only after the
global options.
Revert "Add variable hdevtools_src_dir"

This reverts commit e4b9178f4aefe3e81c4c632d82c1436bc6c167e6.

vim plugins like Syntastic don't use the hdevtools vim functions,
they just call the hdevtools binary and use the g:hdevtools_options
variable, so the separate option g:hdevtools_src_dir isn't considered.

So it's better to add the source dir to the g:hdevtools_options, that
it's also considered by Syntastic.