Convert api functions to autoload-style

Rename the speeddating API functions to use autoload style in
preparation for porting to autoload. Other functions are kept as
script-level functions since they aren't accessed outside of speeddating
(and don't need to be loaded on-demand -- only after the API is loaded).
Convert to use vim's plugin autoload

Move almost all functions into autoload/speeddating.vim and keep maps
and commands defined in plugin/speeddating.vim.

I only converted functions names from script (s:) to autoload
(speeddating#) if they are called from the speeddating api (functions
used in plugin/speeddating.vim).

Unfortunately, if the user uses SpeedDatingFormats (in
after/plugin/speeddating.vim) to define their own formats, the plugin
will be loaded on startup.
Fix first column increment in visual mode

How to reproduce:
:call setline(1, ['0', '', ''])
:execute "normal VG\<C-a>"
Expected:
1
2
3
Actual:
1
 2
 3
Fix for selection=exclusive

To reproduce:
:set selection=exclusive
:call setline(1, '2010-10-10 i am here')
:execute "normal vE\<C-a>"

Expected: 2010-10-11 i am here
Actual:   2010-10-10 ii am here
Defer handling of formats before autoloading

If the SpeedDatingFormat command is used to alter list of supported
formats when autoloading hasn't yet occurred, just save the arguments
into a list for later processing.  This allows deferring the actual
loading until it SpeedDating is actually used, even if custom date
formats are being defined.

If that command is used to get information, either the current list of
formats or usage information, do autoloading and handle that request
immediately.
Move default formats back to plugin file

Definitions of the default formats need to go into the plugin file, not
the autoload file.  If placed in the autoload file, the default formats
will come after formats specified in a user's after/plugin directory
resulting in a behaviour change from previous versions.
Fix permissions
Merge pull request #11 from aschrab/autoload
Privatize function
Consistently indent 2 spaces
Add a README