Added more options

- There are now a few options that you can specify
  - current_file_ext -- limits the search to files that have the current
    buffer's file's extension only
  - current_file_dir -- limits the search to files that are in the current
    buffer's file's directory
  - scmdir -- starts the search at the "root" of a source directory, based on
    the existence of a .git, .scm or .hg dir
  - specific_dirs -- limits the search to these directories

- You can also customize the quickfix mappings
- Each mapping is customizable using a dictionary