Add prefix tree trace

[Ivan Beschastnikh]

Texada currently uses two different trace data types: a linear (vector) trace, and a map trace.

This issue is about adding a third trace data type, the prefix tree. Unlike the linear and map traces, this requires creating a prefix tree data structure. As usual, it requires modifying parsers to parse into prefix trees and creating a prefix tree checker, which will likely be similar to the linear checker.

[Issue created by carolemieux: 2014-07-17]
[Last updated on bitbucket: 2014-08-18]

[Comment created by carolemieux: 2014-08-08]
simple parser and tests added to 6a17064

[Comment created by carolemieux: 2014-08-05]
Checker should check over the entire tree.

[Comment created by carolemieux: 2014-07-23]
checker updated.

[Comment created by carolemieux: 2014-07-23]
fixed memory leaks in rev 779ddd3, need to update checker for shared ptr.

[Comment created by carolemieux: 2014-07-17]
Added prefix tree base (i.e. the prefix tree and prefix tree data structures) to revision 5b4b46d.

[Comment created by carolemieux: 2014-07-18]
Need to make checker check over all traces of a tree w state conservation of some sort. Then refactor with linear checker to remove code duplication.

Also need to remove memory leaks from tests.

[Comment created by carolemieux: 2014-07-18]
Added checker in rev 95f598e

[Comment created by carolemieux: 2014-08-18]
Prefix tree functionality added to main. Ending this issue to create more precise issues.

[Comment created by carolemieux: 2014-08-16]
I have now added a checker that can check over the entire tree. Prefix tree functionality still needs to be added to main.