Embed .lua files into falco executable

Instead of having .lua files external to the program responsible for
loading rules, embed the contents of those files into the executable
and load them as strings instead of as files:

Add a cmake custom command below userspace/engine/lua that calls a
bash script lua-to-cpp.sh to generate falco_engine_lua_files.{cpp,hh}
that are compiled into the falco engine library.

The script creates a .cpp file that has const char * symbols for each
file, as well as lists of files that should be loaded when the falco
engine is loaded. There are actually two lists:

- lua_module_strings: these are loaded and also added to the lua
  runtime package.preload table, so they are available when lua code
  require()s them.

- lua_code_strings: these are loaded *and* evaluated, so the functions
  in them are availble to be called from C++.

This simplifies some of the falco_common methods, as there's no need
to keep track of a "main" lua file to load or paths from which the lua
loader should find files for modules, and there's no need to keep
track of an "alternate" lua directory that occurs for debug builds.

Also, there's no need to include any .lua files in the installed
packages, as they're built into the falco binary.

Signed-off-by: Mark Stemm <mark.stemm@gmail.com>

userspace/engine/falco_engine.cpp

@@ -53,7 +53,7 @@ falco_engine::falco_engine(bool seed_rng, const std::string& alternate_lua_dir)
 	luaopen_lpeg(m_ls);
 	luaopen_yaml(m_ls);
 
-	falco_common::init(m_lua_main_filename.c_str(), alternate_lua_dir.c_str());
+	falco_common::init();
 	falco_rules::init(m_ls);
 
 	m_required_plugin_versions.clear();