Replace config setters/getters with something generic

[klange]

Probably a set command line in Vim.

Also, replacing the current bimrc format with a script containing commands would be a good way to unify things.

[klange]

These are the current setters/getters:

• colorgutter, global, boolean
• indent/noindent, buffer, boolean
• theme, global, colorscheme name
• splitpercent, global, integer
• syntax, buffer, syntax highlighter name
• tabs/spaces, buffer, boolean
• tabstop, buffer, integer (>0, <32)
• padding, global, integer
• smartcase, global, boolean
• hlparen, global, boolean
• hlcurrent, global, boolean
• crnl, buffer, boolean
• numbers, global, boolean
• relativenumber, global, boolean