Converted to Maven project

Converted to Maven project
Merge pull request #1 from sboyina/mavenize

Converted to Maven project
Merge pull request #12 from sboyina/master

Converted to Maven project
Allow nested expression using the with() method, e.g. with("3*x+y")
Allow nested expression using the with() method, e.g. with("a", "3*x+y")
Merge branch 'master' of https://github.com/uklimaschewski/EvalEx.git
Merge branch 'upstream-master'.
Added missing source version to pom.xml
Updated the Nested Tests to test for circular expressions.
Added recursion limit for circular arguments in Expression class