Added Substring function

[ChrissW-R1]

Based on the changes of #207 added support of the function substring with syntax SUBSTRING(... FROM ... FOR ...)

See also:
http://sqlzoo.net/wiki/SUBSTRING%28ansi%29

[coveralls]

Coverage decreased (-0.002%) to 83.565% when pulling 8711734 on conterra:substring into 3bc316d on JSQLParser:master.

[coveralls]

Coverage decreased (-0.002%) to 83.565% when pulling 9025b6f on conterra:substring into 3bc316d on JSQLParser:master.

[coveralls]

Coverage decreased (-0.002%) to 83.565% when pulling a9fcd45 on conterra:substring into 3bc316d on JSQLParser:master.

[coveralls]

Coverage decreased (-0.002%) to 83.565% when pulling 65e2bf2 on conterra:substring into 3bc316d on JSQLParser:master.

[wumpz]

I see you already divided the first pull request. I will look into this.

[wumpz]

already solved