Juliet

Added
- Upgraded list of contributors.
- `tests` folder where code tests will be saved.
- `zeus` sampler thanks to contribution from Rachel Cooper.
- Secondary eclipse fitting thanks to contribution from Jayshil Patel.
- Additional GP kernels thanks to contribution from Jonas Kemmer.
- Added lowercase priors (thanks to rosteen; 80).
- Option to activate/deactivate HODLR solver when using `george` GP kernels.

Fixed
- Bug when multiple planets using and not `efficient_bp` thanks to tronsgaard.
- Keywords that made `juliet` incompatible with `dynesty` 1.2.2 (this makes `juliet` incompatible with pervious `dynesty` versions)
- `exponential` prior which was not working.
- Problem with `dynesty`, whose newest version crashed with `juliet`.

Removed
- Removed the `juliet.py` (and associated `utils.py`, `FLAGS.md`) which hosted the original version of the code, to not confuse contributors.

Fixed
- Supersampling bug when evaluating models.

Removed
- Files for pink noise in deference of building a new package.

Fixed
- Error on importing `__init__.py` after new versioning file.
- All `np.int` calls have been changed for `int` calls.

Added
- Support for multithreading with `emcee`.
- Added `stepsampler_ultranest` to use Ultranest's stepsampler (see https://johannesbuchner.github.io/UltraNest/example-sine-highd.html).
- `setup.py` automatically installs `ultranest` and `emcee` now, as both are supported by `juliet`.
- Added canonical `_version.py` file to store versions of the code, following user Zooko in stackoverflow question 458550. Modified `__init__.py` and `setup.py` accordingly.
- Added `test_juliet.py` script to give `juliet` a test run with all the samplers.

Fixed
- `juliet.fit` docstring parsing.
- Bug when both `input_folder` and `out_folder` are given, introduced by the addition of support to `emcee`.

Added
- PR 47, which adds function to `juliet.utils` to read AstroImageJ tables.
- PR 22, which started a unit test script (`test_utils.py`); also added a `.gitignore`.
- Created `CHANGELOG.md` (this file).
- Deprecated the use of several flags (e.g., `use_dynesty`, `use_ultranest`, `dynamic`, etc.); now samplers can be selected using the `sampler` string via `juliet.fit`. Options for each sampler can be directly ingested to `juliet.fit` via `**kwargs`.
- Outputs from multinest are kept in the output folder now (were removed in previous juliet versions).
- Support for `emcee`.

Fixed
- Fixed bug that was making `juliet` runs with `dynesty` always go to Dynamic Nested Sampling by default.
- Bug that made the `juliet.utils.get_all_TESS_data()` call to download _all_ files. Now by default only lightcurves are downloaded.
- Refactored the `juliet.fit` class of the code; much easier to read, much easier to pass arguments around, much easier to implement new samplers.
- Removed the `delta_z_lim` flag which didn't do anything; the `delta_z` limit can be inputted through the `kwargs` via `juliet.fit`.