Incorporate PCRE library; make more use of regex

There are a number of instances of pattern matching in MaxScale, such as analysis of options from the configuration file. Code could be reduced and made more elegant by use of regular expressions. In addition, matching could be made more flexible e.g. by allowing white space around options. The PCRE library is available at http://www.pcre.org/ and is free to use.

All use of the POSIX regex should be replaced with the use of the bundled PCRE2 library.