Behavior when dealing with whitespace is improved.

* If origin column is solely whitespace, then the column selection will ONLY
  include whitespace.

* If origin column is not solely whitespace, then the cursor will be set to the
  beginning of the word on each line when checking for boundaries, so that
  whitespace is not mistakenly included in the boundary assessment.

Movements where throw off because they work with screen columns, but not all
calculations were done using screen columns.

The plugin should now work as expected on lines with tabs, and also multibyte
characters.

Fixes #1

Switched to iteration.

Fixes #4

Vimhelp uses || to show links (and conceals the characters). Delimit the
table as code so the bars show up as intended.

The file should be regenerated by the user.

With the cursor on "ab", I get an invalid selection that extends to the "." of the second line (and a beep when smart boundaries are used), instead of the expected selection of lines 3 + 4.

" Use real visual mode mappings to avoid the mapping delay when entering visual
" mode with "v".
xnoremap <silent> ab :<C-u>call TextObjWordBasedColumn("aw")<cr>
xnoremap <silent> aB :<C-u>call TextObjWordBasedColumn("aW")<cr>

This can be fixed by checking that there's actually a character at the start virtual column. The match for the exact column number also ensures that if the position is inside a Tab or in the middle of a double-width character, the selection will not be extended.

This matters when there are multi-byte, unprintable, or Tab characters, in which cases the virtual (screen) column is not equal to the byte index.
Need to pass both columns to the s:find_boundary_row() function.

The normal mode mappings that start with "v" introduce a mapping delay when entering visual mode; this is irritating. Instead, define the mappings directly in visual mode, and disregard the previous selection with <C-u> prepended to the function call, so it works the same.