Repobee

This is just a hotfix for documentation, dependencies and some improved error messages.

Documentation
* d2daa56 Remove incorrect note about peer review support, fix 374
* a908794 Point RTD config to correct requirements file, fix 375

Other
* 1ee1550 Improve error message on plugin load errors, fix 377
* 87dce4d Emit a warning if REPOBEE_TOKEN overrides config value, fix 376

This release brings full compatibility with GitLab, along with a bunch of GitLab-specific fixes and improvements. There are a few fixes and quality-of-life improvements for GitHub as well, along with the removal of a dependency that required gcc to be built.

Features
* 398be85 Add check on the base url in GitHubAPI (371)
- Only `https://api.github.com` and enterprise urls ending with `/api/v3` are now allowed. Forgetting the `/api/v3` caused many errors, as PyGithub handles that strangely.
* 47fe1df Add GitLab compatibility for check-reviews command (360)
* 65a461d Add GitLab compatibility for end-reviews command
* a5792b7 Add GitLab compatibility for assign-reviews command (352)
* 47c63ba Add GitLab compatibility for verify-settings command (348)

Bugfixes
* 584bd2e Fix bad error message on invalid keys in config, fix 372
- The new error message includes where the file is located, allowing a user to remove the offending keys manually
* 3223499 Fix assignees not assigned to peer review issues (GitLab)
* 792be65 Fix KeyError when student repo is missing in assign-reviews (GitLab) (365)
- There is still an error, but it's an intended early exit!
* 9068e7f Fix fetching/setting of issue body for GitLab (358)
* d8a6275 Parse raw created_at attribute in GitLabAPI to datetime.datetime (357)

Documentation
* 426baaf Touch up formatting
* 3eb69f2 Update GitLab-related documentation for v2.3.0 release
* 688b199 Add repobee-feedback to list of plugins
* 14c9f23 Fix typo, fix 349
* b706b5d Add development environment setup guide (344)

Refactorings
* f5adada Remove dependency on maya (370)
- This also removes the dependency on `regex`, which needed to be built using gcc, so RepoBee should now be easier to install.
* e8627d2 Move SystemExit calls from cli module to main module (363)
* 543a7fb Refactor requirements in .txt files and setup.py (343)

Other
* 0de5c80 Update upcoming features section of README

Deprecations
* e9d05fd Correct access token terminology (341)
- Among other things, this replaces the environment variable `REPOBEE_OAUTH` with `REPOBEE_TOKEN`
- `REPOBEE_OAUTH` is still recognized, but a warning is emitted telling users to swap over

Documentation
* a3046d6 Fix broken link in clone docs, fix 340

Refactorings
* 75fb4e0 Only register plugins that are not already registered 339
* aad5abd Have output from --version just be the version number 339
* a2294c8 Don't convert verify-settings errors to SystemExit, fix 337
- This is feature-impacting, as error messages from verify-settings now propagate properly to the user
* e9d05fd Correct access token terminology (341)
* 34799d7 Wrap python-gitlab exceptions in RepoBee exceptions (336)
- This also improves error messages to the end user
* 61345a2 Move token env variable parsing to config module (334)

Other
* e61742b Fix URLs in broken update tests, fix 335
* ed4179d Add system tests for update command, fix 240

Features
* 89a5f2e Add basic hook results query command (333)
- The `query` plugin adds the experimental query command, that essentially replays hook results stored in a hook results file
* 207a5f2 Add possibility for ext commands to request base parsers (331)
- For example, extension commands can now request the `plug.BaseParser.STUDENTS` parser to automatically get the `--students` and `--students-file` options added.
* 583f03f Add --hook-results-file option to list-issues command (330)
* d4323c8 Add option to write clone command hook results to JSON file (328)
- With the `--hook-results-file` option
* 44d7d8a Use persistent logfile, fix 322
- Previously, RepoBee would spit out logfiles all over the place. The persistent logfile is located in the user log directory (typically in `~/.cache/log/repobee/repobee.log` on a Linux system).

Documentation
* 27d1492 Add list of curated plugins, fix 169
- The list can be found [here](https://repobee.readthedocs.io/en/stable/plugins.html)
* c2dee68 Add reference to the RepoBee ITiCSE paper

Refactorings
* c84abac Move the Review tuple to repobee-plug, fix 327
* 7453331 Move name generation functions to repobee-plug (332)
* 44bb9e9 Execute config hooks before instantiating ext commands

Other
* 61f84d9 Add a CONTRIBUTING.md, fix 128

Security
* 92aa5cf08cc08d2647a9f22bb6ff120cd5a88360 Filter out secure token from `show-config` command output