Add only_in_current_directory option to buffer source

[youxkei]

When vim has the following state:

• current directory: /tmp/dir
• buffers
  • No Name
  • /tmp/foo.txt
  • /tmp/dir-or-not.txt
  • /tmp/dir/bar.txt
  • /tmp/dir/foo/bar.txt

the buffer source with only_in_current_directory enabled lists the following buffers:

• /tmp/dir/bar.txt
• /tmp/dir/foo/bar.txt

The buffer source with only_in_current_directory enabled is useful when you use it combined with file/rec as following:

call denite#custom#alias('source', 'buffer/cd', 'buffer')
call denite#custom#var('buffer/cd', 'only_in_current_directory', 1)

" combine buffer/cd with file/rec
:Denite buffer/cd file/rec

[Shougo]

This option is not needed. Because matcher/project_files already exists for it.