Handle/specialfunctionkey

hi supasorn

I added InitSpecialMappings function & added easymotoin prefix key to special functions

Now you can map special function key by vimrc
example:
```vim
    let g:EasyMotion_special_mapping_l = 'L'
    let g:EasyMotion_special_mapping_p = 'p'
```
and by default, vl, yl and dl conflict with default vim functoin, so add
easymotion_leader_key to special function(you can use special function
by type `d<Leader><Leader>l)