Add smart leaves to checkbox by Noel Henson.

From a message to the mailing list on August 28, 2008.
Add weighted checkboxes by Noel Henson.

From a message to the mailing list on September 16, 2008.
Make faster checkboxes by Noel Henson.

From a message to the mailing list on September 9, 2009.
Disable faster checkboxes.

The new faster method only considers the immediate lower level of the
headline that's being calculated. So, on the following outline:

[_] % Root
	[_] a
		[_] b
		[X] c
	[X] 100% d

With the old behaviour the percentage of Root would be 75% after
calculations, while the new faster one would find a value of %50.
Use :noremap <silent> and <bar> for vo_checkbox.
Merge branch 'checkbox' into 0.3.7
Restore tags plugin.
Support checkboxes in tags.
Add tags plugin to vimoutlinerrc.
Add math plugin by Noel Henson.

From a message to the list on October 20, 2008.
Remove filetype load guard.
Add math plugin to vimoutlinerrc.
Add float and eval load guard to math plugin.
Fix white space on vo_math.vim.
Fix new calculation method for checkboxes.

The new method behavior differed on the way it counted checkboxes
without percentage depending on whether they were up or down on the tree
from the current checkbox.

Now it'll calculate the same way up and down the tree from the current
branch.
Make new checkbox calculation method optional.
Merge branch 'development' into 0.3.7
Make the faster checkboxes method the default.
Fix mappings of checkbox.
Add newhoist plugin by Noel Henson.

From a message to the list on September 15, 2009.