Support stripped down versions of Vim

Closes #6.
Change undodir regex conditional

undodir is set to '.' by default.

'^\.\%(,\|$\)' will accept the default and if '.' if the first on a
list, the option is set, as intended.
Don't butcher filename in last viminfo argument

Closes #10.
Add instructions for overriding
Explain how to find out what the plugin does

References #7.
Document unintuitive settings

Closes #7.
Concede 'list'

Closes #5.
sensible.vim 1.0
Set infercase
Don't force UNIX line endings on Windows

Closes #14.
Set shiftround

Confession: I only recently found this, but I've wanted it for years.
Nobody wants to shift from 11 to 3 spaces, right?
Drop 'fillchars'

Closes #15
Remove infercase

Closes #17.  I'll battle ignorecase in a separate plugin.