Update CI and Documentation to Restore Functionality from Travis

[egordon]

Since the move to Github Actions in (#598), some CI functionality has been lost.

This includes:

• Codecov support
• Checking formatting prior to merging

In addition, the simultaneous update to Ubuntu Focal has lead to outdated documentation and unused CI code.

This PR re-adds this lost functionality, cleans up the CI code by removing old statements, and updates the main README to reflect the current use on Ubuntu Focal.

Unfortunately, this has also necessitated an upgrade to clang-format-10, which is available on Ubuntu Focal.

The previous version of clang-format-6.0 had a bug such that the output of output-replacement-xmls (which we used to check formatting) did not match the actual replacements made in-file.

The new clang-format-10 adds a --dry-run flag which offers the exact functionality we want (i.e. error if formatting is required).

---

Before creating a pull request

• [ N/A ] Document new methods and classes
• [x] Format code with make format

Before merging a pull request

• [x] Set version target by selecting a milestone on the right side
• [ ] Summarize this change in CHANGELOG.md
• [x] Add unit test(s) for this change

[codecov[bot]]

Codecov Report

Merging #610 (4ee7897) into master (62dfb15) will increase coverage by 0.76%. The diff coverage is 76.68%.

:exclamation: Current head 4ee7897 differs from pull request most recent head 38e46ba. Consider uploading reports for the commit 38e46ba to get more accurate results

@@            Coverage Diff             @@
##           master     #610      +/-   ##
==========================================
+ Coverage   75.59%   76.35%   +0.76%     
==========================================
Files         243      200      -43     
Lines        5856     7030    +1174     
==========================================
+ Hits         4427     5368     +941     
- Misses       1429     1662     +233     

Impacted Files	Coverage Δ
include/aikido/common/BSpline.hpp	100.00% <ø> (ø)
include/aikido/common/RNG.hpp	100.00% <ø> (ø)
include/aikido/common/Spline.hpp	100.00% <ø> (ø)
...clude/aikido/common/detail/ExecutorThread-impl.hpp	100.00% <ø> (ø)
include/aikido/common/detail/Spline-impl.hpp	96.96% <ø> (+0.22%)	:arrow_up:
include/aikido/common/detail/algorithm-impl.hpp	100.00% <ø> (ø)
...lude/aikido/common/detail/metaprogramming-impl.hpp	80.00% <ø> (ø)
include/aikido/common/detail/pair-impl.hpp	100.00% <ø> (ø)
include/aikido/constraint/Differentiable.hpp	100.00% <ø> (ø)
...clude/aikido/constraint/DifferentiableSubspace.hpp	100.00% <ø> (ø)
... and 253 more