Use new rust-bindgen crate for faster builds

Rather than cloning the bindgen repository and building from source, use
the packaged crate. The result is the rebuilds are much, much faster.
Also, had to make numerous changes for the new version of bindgen.

cargo test passes

vagrant/ubuntu14/Vagrantfile

@@ -1,9 +1,9 @@
 #
-# Vagrantfile for Ubuntu Linux 14.04 test environment.
+# Vagrantfile for Ubuntu Linux 16.04 test environment.
 #
 Vagrant.configure(2) do |config|
 
-  config.vm.box = 'ubuntu/trusty64'
+  config.vm.box = 'ubuntu/xenial64'
 
   # need enough memory to build syntex_syntax crate
   config.vm.provider 'virtualbox' do |vb|