Jia Sui

I use OS X 10.11.3 + mavim, this setting works for me. ``` let g:clang_library_path="/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib" ```

Thanks for the contribution, but I can't merge it right now. This PR is still too rough. 1. It breaks on neovim. 2. It only support ctags, I wish it...

Oh, this PR is releated to #44, BTW

You should use `gen_tags#opt_converter()` to convert the option (list and string are both supported)

The gtags can use the file list as below ```bash rg --files | gtags -f - ```

There is no need to add 'cmd' or 'sh' The command can work directly, for example ```vim call jobstart(['rg', '--files', '|', 'gtags', '-f', '-']) ```

you can't redirect the stdout in `job_start`, because the stdout of job_start only appear in callback function.

I tried this code snippet, it works on windows and linux with vim8.1/neovim ```vim function! s:job_stdout(job_id, data, ...) abort if type(a:data) == 1 "string echomsg a:data elseif type(a:data) == 3...

 oh... I got this error..

I add a stderr callback to print the error message. I tried your code, it works with `git ls-files`, I don't have `rg` installed so I don't test with rg....