Add benchmarking & some opti

[artivis]

• Add benchmark
• some small opti
• SE2Tangent::rjacinv/ljacinv
• SE_2_3Tangent::rjacinv/ljacinv
• fix average unit test
• run tests in debug and release on ubuntu.

This PR adds some micro benchmarks using Google benchmark. This allows to have some time-based benchmarks on a per-function basis so that one can compare different implementations.

The PR also contains numerous small optimizations, most of which do not actually show any benefit in the aforementioned benchmark. Those which do are listed below.
Most noticeably, implementing SE2Tangent::rjacinv/ljacinv (~6x / ~4.3x) and SE_2_3Tangent::rjacinv/ljacinv (~4.5x / ~5x) are a big win.

It also remove some unnecessary cmake warning suppression for the test/examples, fix the average unit test that was disabled and finally it runs the unit test both in Debug and Release on Ubuntu.

Some numbers obtained through the benchmarking introduced in this PR:

Group	Operation		Before		After
SE2	rjacinv
(mean)			49.6 ns		8.41 ns
(median)			49.6 ns		8.39 ns
(stddev)			3.69 ns		0.102 ns
	ljacinv
			37.1 ns		8.48 ns
			37.3 ns		8.46 ns
			3.77 ns		0.097 ns
SE_2_3	rjacinv
			1570 ns		349 ns
			1539 ns		354 ns
			72.8 ns		9.76 ns
	ljacinv
			1722 ns		338 ns
			1706 ns		337 ns
			68.4 ns		11.0 ns
	adj
			100 ns		76.1 ns
			100 ns		75.8 ns
			1.11 ns		1.45 ns

As a bonus, here is compared the unit quaternion random implementation from Eigen and the one proposed in #105. Note that currently manif still uses the implementation from Eigen as I don't see a strong motivation to introduce some new code to support for a non critical function. Rather than changing manif implementation I'd suggest to propose the change directly upstream to Eigen.

	Operation		Before		After
quaternion	random
			524 ns		491 ns
			523 ns		490 ns
			2.04 ns		1.99 ns

[artivis]

Full disclaimer, I did not actually run the math for SE_2_3Tangent::rjacinv/ljacinv. I naively/straightforwardly applied the pattern I saw in SE3Tangent::rjacinv/ljacinv and the tests passed :)

[joansola]

In what consist the optimizations on ljacinv, rjacinv, etc?

[artivis]

In what consist the optimizations on ljacinv, rjacinv, etc?

SE2Tangent::rjacinv/ljacinv and SE_2_3Tangent::rjacinv/ljacinv?
Well before they were implemented as the inverse of the respective Jacs (e.g. se2.rjac().inverse()) whereas this PR actually implements their analytical closed-form (straight to se2.rjacinv()).

[joansola]

Oh OK I see. Yep, obviously much faster!

[codecov]

Codecov Report

Merging #227 (ca61008) into devel (287c71e) will decrease coverage by 0.14%.
The diff coverage is 97.18%.

@@            Coverage Diff             @@
##            devel     #227      +/-   ##
==========================================
- Coverage   98.05%   97.90%   -0.15%     
==========================================
  Files          48       49       +1     
  Lines        1436     1531      +95     
==========================================
+ Hits         1408     1499      +91     
- Misses         28       32       +4     

[artivis]

@joansola This PR is ready when you are. Nevermind the failure coverage test nor the pending ones (looks like a bug).

[joansola]

OK I already had a look to all this some time ago, I approve right away