Add --max-filesize option to cli

The --max-filesize option allows filtering files which are larger than
the specified limit. This is potentially useful if one is attempting to
search a number of large files without common file-types/suffixes.

See #369.

build.rs

@@ -2,6 +2,7 @@
 extern crate clap;
 #[macro_use]
 extern crate lazy_static;
+extern crate regex;
 
 use std::env;
 use std::fs;