Use simpler build revision approach.

I deleted my CMake cache, and CMake would no longer find Git, though I
had it installed in my Program Files (x86) folder beside CMake.

The new approach doesn't require Git, it just reads the HEAD revision ID
and shortens it to 8 characters.
Fixed CEF linker error.

The error manifested after upgrading to CEF 3.2171.1902.
Corrected comment.
Disabled CEF's built-in spell checker.

It's unnecessary, and LOOT disables the context menu anyway.
Minor corrections to build instructions.
Updated CEF used, removed Encoding API shim.

The new CEF release branch is based off Chromium 39, so has native
support for the Encoding API.
Updated JS libraries.

Jed, Jed Gettext Parser and RequireJS have been updated to 1.1.0, 1.0.0
and 2.1.15 respectively. The RequireJS order plugin has been removed, as
it shouldn't actually be used with RequireJS 2.

This change may cause JS undefined object errors (see #327), but I
didn't experience any.
Updated Boost and Libgit2 versions used.