cmd-key-happy: build fix for Mavericks
mavericks: update README

If you upgrade to Mavericks you'll get the following error "failed to
create event tap!" when cmd-key-happy starts.  The granularity of
using the accessibility APIs, which is what cmd-key-happy depends on,
is now much finer.  To fix this: Go to "System Preferences", "Security
and Privacy", "Accessibility" and from there you'll need to drag+drop
the applications (via the Finder) into the approved list.
Fixed launching of cmd-key-happy via launchd on Mavericks

Added an additional step for the installation on Mavericks.  The
makefile rule 'install-security-exception-for-cmd-key-happy' now updates
the database which governs which applications can use the accessibility
APIs.

On Mavericks, as noted in the install file, the installation procedure
is now:

  $ make install
  $ make install-rcfile   # only if you have no ~/.cmd-key-happy.lua
  $ make install-security-exception-for-cmd-key-happy
  $ make install-plist

Closes github issue #12.
Added bug: install procedure needs revamping
INSTALL: deprecated note about setting the terminal type

The original commentary dates back to Leopard and is no longer relevant
on Mavericks.
Another go at fixing launching of cmd-key-happy via launchd on Mavericks

Complementary commit is 65976a6ccfe1670997521ad5536bb6f21e3274bf.  That
commit did allow cmd-key-happy to work when restarted, but not when the
machine was rebooted.  Calling AXAPIEnabled() appears to be very
necessary if the machine has rebooted, so sticking with this call until
an alternative truly becomes necessary.

Really really trying to close issue #12.
Mavericks: rework installation notes

Updated instructions for installing on Mavericks. The key thing is to
make restarting cmd-key-happy use launchctl as this ensures that it is
"cmd-key-happy" that is wanting Accessibility access and not "Terminal".

Addresses issues #11, #12, #13 and #14.

Signed-off-by: Andrew McDermott <andrew.iain.mcdermott@gmail.com>