Added a config variable that disables the mappings

This is a slick little plugin! I really like it.

However, I didn't care for the default mappings. I have <leader>f already set in my vimrc, and worse, in my muscle memory!

Anyway, this addition wont make any difference to current users, but if you set g:foldsearch_disable_mappings to 1 then the mappings aren't applied and you can use the plugin with your own mappings or via commands.

Thanks for the plugin!