Major iteration counting

[ewu63]

Addresses #21 by:

1. calling the SNOPT routine snkerc instead of snoptc
2. writing a custom snstop code in Python to replace the one supplied by SNOPT, and called every major iteration
3. wrapping the snstop Python code with f2py and passing it into snkerc since snoptc accepts much fewer inputs
4. modifying the db file structure such that the flag isMajor is set to true when the evaluation is at a major iteration
5. updating optview accordingly to filter iterations based on this flag

A few additional changes:

1. added code to retrieve the approximate Hessian from the SNOPT work array. Note this only works when full-memory Hessian option is used, as the memory layout in SNOPT is different otherwise
2. added code to retrieve the full vector of penalty parameters, containing entries for each of the constraints
3. storing these in the db file along with several other entries that could potentially be useful for users. The full list can be found in snstop and can be modified as needed, and it is straightforward to add more. Note that these entries are only present for major iterations.