Add speed limiter class

[chapulina]

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🎉 New feature

Summary

We've been using the SpeedLimiter class ported from ros_control on Ignition Gazebo's diff drive controller for a while. Now another controller is being added and wants to use the class too (Ackermann on gazebosim/gz-sim#618), so it's good to move it to a common place where it can be reused by various controllers instead of copied. Ignition Math feels like a good place to put this.

The class had originally been copied from ros_control without much testing. While porting it to ign-math, I added tests and noticed that the jerk limit calculation was mistaken and is being fixed on ros-controls/ros_controllers#388. I believe the version on this PR should be correct.

Some other changes:

• Made limits +1inf by default
• Using chrono for time

Test it

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[codecov]

Codecov Report

Merging #194 (7a97a73) into ign-math6 (b84710d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           ign-math6     #194   +/-   ##
==========================================
  Coverage      99.20%   99.21%           
==========================================
  Files             63       65    +2     
  Lines           6019     6087   +68     
==========================================
+ Hits            5971     6039   +68     
  Misses            48       48           

Impacted Files	Coverage Δ
include/ignition/math/SpeedLimiter.hh	100.00% <100.00%> (ø)
src/SpeedLimiter.cc	100.00% <100.00%> (ø)

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[chapulina]

@scpeters , I refactored the API, implementation and naming conventions. I think the class is easier to use and the math is more straight forward now. Let me know what you think.

[scpeters]

sorry for the delay in getting back to this. thanks for addressing my earlier comments; I have a few more now

[scpeters]

I think the code is clearer to read this way, but I believe it may have been written the other way to avoid a division operation and divide by 0 concerns

[chapulina]

Yeah I agree that this may have been the motivation. One lesson I took from the fact that the math had been wrong on the ros_control implementation all this time is the value of readability. I'm leaning towards leaving the math straightforward so it's easier to debug in the future. I added tests for the dt == 0 case, so I think we're covered.