Fixed #38

Added a mapping `<Plug>(table-mode-sort)` which is mapped by default to
`<Leader>ts` that sorts the current table by the column in which the
cursor is currently.

Also added `TableSort` command that gives you a little more control over
the sorting, you can pass in additional :sort flags like u, i, n etc and
also use it with a `!` to sort in reverse order.

autoload/tablemode/spreadsheet.vim

@@ -179,3 +179,11 @@ function! tablemode#spreadsheet#Average(range, ...) abort "{{{2
   call insert(args, a:range)
   return s:Average(call('tablemode#spreadsheet#cell#GetCellRange', args))
 endfunction
+
+function! tablemode#spreadsheet#Sort(bang, ...) "{{{2
+  let opts = a:0 ? a:1 : ''
+  let bang = a:bang ? '!' : ''
+  let [firstRow, lastRow] = [tablemode#spreadsheet#GetFirstRow('.'), tablemode#spreadsheet#GetLastRow('.')]
+  call tablemode#spreadsheet#MoveToStartOfCell()
+  exec ':'.firstRow.','.lastRow . 'sort'.bang opts '/.*\%'.col('.').'v/'
+endfunction