Add support for client-side Lua execution

This update extends the .lp preprocessor to add support for new opening tags: <?lua@client, <?lua@server, and <?lua@both. The tag <?lua@client converts the code to client-side Lua, <?lua@server works the same as <?lua or <?, and <?lua@both allows to mix client and server-side Lua code. To make the client-side Lua usage possible, this Sailor update integrates a Lua VM in JavaScript, extended to allow usage of browser-specific JavaScript objects (such as document, window, etc) from Lua.