Adding tracking of arbitrary test parameters

[barbehenna]

I implemented a set of *_xl functions (one for each tinytest expect_* method) that append any extra parameters to the attributes of the test results. There's also a method, makeDataFrame, that can collect these arbitrary test attributes and return a data.frame.

[codecov]

Codecov Report

Merging #2 into master will decrease coverage by 51%.
The diff coverage is 0%.

@@          Coverage Diff          @@
##           master    #2    +/-   ##
=====================================
- Coverage      85%   34%   -51%     
=====================================
  Files           2     4     +2     
  Lines          20    50    +30     
=====================================
  Hits           17    17            
- Misses          3    33    +30

Impacted Files	Coverage Δ
R/expectations.R	100% <ø> (ø)	⬆️
R/expectations_xl.R	0% <0%> (ø)
R/methods.R	0% <0%> (ø)

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[eddelbuettel]

Really nice work -- thank you!