[REQS-329] Created cross-gamma calculator for single curve. Added related tests.
Merge branch 'develop' into topic/reqs-329
[REQS-329] Clean comments on test.
[REQS-329] Added code to produce swap gamma analysis in the tutorial package.
[REQS-329] Added documentation for the cross-gamma calculator.
REQS-329 Resolving merge issue back onto develop
Merge branch 'topic/reqs-329' into develop