reading material about 17.2 page395:
http://www.lua.org/pil/6.3.html proper tail call
17.3 goto:
http://coolshell.cn/articles/11112.html
18.2 page420, could refer to the project that Google open sourced.
https://developers.google.com/protocol-buffers/docs/tutorials
18.2 page420, F# pattern match
http://en.wikibooks.org/wiki/F_Sharp_Programming/Pattern_Matching_Basics
19.6 page458. refer to CodeMaid source code
internal static int CalculateComplexity(CodeElement element)