[PLAT-6363] Improved root finder in Carr-Lee model

Reviewed by Stuart.
[PLAT-6500] Greek calculators for FX volatility swaps

Finite difference approximation is used.
Reviewed by Vince.
[PLAT-6509] Integration of Carr-Lee Greek calculators

Reviewed by Vince.
[PLAT-6518] Test new properties in fair value calculator

Reviewed by Stuart W.
[PLAT-6520] Summarize tests for Greek calculator

Also include [PLAT-6518].
Reviewed by Stuart W.
[PLAT-6519] Handle singular integrands

Reviewed by Stuart W.
[PLAT-6513] Add constructor specifying strike range

Reviewed by Stuart W.
[PLAT-6516] Consistency between fair value calculator and Greek calculator

Reviewed by Stuart W.
[PLAT-6524] Year fraction for vol swaps should be based on 252

Reviewed by Stuart W.
[PLAT-6512] Fix historical realized variance calculator

Reviewed by Stuart W.
[PLAT-6524] Year fraction based on 252
[PLAT-6521] Exposed remaining fx vol swap functions to engine; fixed theta function to use the correct calculator.
[PLAT-6521] Added currency to PV and greeks (Ian).