Add vim-vinegar plugin
Massive vimrc changes

- Set leader to ";" and use leader in ";" mappings
- Add mappings for split window open and sourcing vimrc
- Overwrite functions (when reloading vimrc)
- Add abbreviations
- Add operator-pending mappings
- In insert mode, remap jk to <Esc>, remap <Esc> to <nop>
- Group all autocommands and clear augroups to prevent duplicate autocommands
- Add shortcuts to plugin mappings
- Add customized statusline
- Use local settings in Settabbing function and FileType for autocommands