Rapidtide

* (rapidtide) Added a new method for generating global signal using PCA.
* (all) Further imports from master branch to improve deployment.
* (simdata) Complete overhaul - new parser better checks, more flexible input formats.
* (io.py) Improvements to readvecs to handle very large files.
* (ccorrica, filttc, histtc, pixelcomp, resamp1tc) Facelift, cleanup, new parsers.
* (testing) Removed python 2.7 CI build.
* (all) Addressed many linter issues, updated deprecated numpy and scipy calls.

* (all) readvectorsfromtextfile now handles noncompliant BIDS timecourse files.
* (happy) Fixed a very subtle bug when an externally supplied pleth waveform doesn't start at time 0.0 (fix to issue 59).
* (filttc, histtc, showarbcorr) parser improvements.

* (package) Copied Taylor Salo's improvements to build and deployment from the master branch.
* (all) Ran all python files through Black to give consistent formatting (really, truly this time).
* (all) Implemented new, generalized text/tsv/bids text file reader with column selection (readvectorsfromtextfile).
* (atlastool) Fixed some import and syntax issues with numpy.
* (showarbcorr) New program to do crosscorrelations on timecourses with different samplerates.
* (happy) Fixed column selection bug with BIDS files.
* (happy) General formatting improvements.
* (dlfilter) Made diagnostics more informative to help get dlfilter enabled.

* (all) Fixed readbidstsv calls.
* (all) Beginning a rethink of a universal text timecourse reader.
* (happy) Added new tools for slice time generation.

* (rapidtide) Rolled back default similarity metric to 'correlation' from 'hybrid'. 'hybrid' works very well most of the time, and fails strangely occasionally. When 'correlation' fails, it does so in more predictable and explicable ways.
* (happy) Restored functionality and options for motion regression that I broke when separating out the command parser.
* (tests) CircleCI config files changed to keep tests from stepping on each other's caches (thanks to Taylor Salo).

* (package) Ran all python files through Black to give consistent formatting.
* (rapidtide) Did some prep work to implement echo cancellation.