Various Improvements

[varunagrawal]

1. Suppress maybe-uninitialized warnings from Eigen for Release build. We only see this warning in Eigen, and since this is a vendored version, the assumption is that the original developers have already accounted for this to not be a problem.
2. Fix some docstrings.
3. Use resetIntegration to initialize the ImuFactor and CombinedImuFactor classes.
4. Wrap ImuFactor2.
5. Added a new macro GTSAM_COUT which is for classes/types that don't have a .print() defined or have the << operator overloaded. An example usage is below:

Rot3 wRb = Rot3();
GTSAM_COUT(wRb);

which prints

wRB: 1, 0, 0  // Note that it also prints the variable name similar to GTSAM_PRINT.
0, 1, 0
0, 0, 1

Interestingly, there is no CombinedImuFactor2 which works on NavStates. This should be a TODO for us given the recent importance of NavState.

[varunagrawal]

@dellaert reminder

[dellaert]

But print already assumes cout

[varunagrawal]

This is more for types that don't support .print(). I can use this to print doubles, strings etc.

[dellaert]

Then just use std::cout, please.

[varunagrawal]

Wouldn't it be convenient to do GTSAM_COUT(x) instead of std::cout << "x: " << x << std::endl;?

[dellaert]

Not a GTSAM thing