Lexi-bu

Mostly modified the documentation to reflect the changes because of renaming `lexi` to `lexi_bu`

**Full Changelog**: https://github.com/Lexi-BU/lexi/compare/v0.3.3...v0.3.4

Mostly minor edits to the Readme.md file. Changed the way the images were being displayed. Now they use GitHub raw user content link instead of the local file locations.
Added `lexi` to readme.
Added `doi` from `Zenodo`.
Added details about citations.

**Full Changelog**: https://github.com/Lexi-BU/lexi/compare/v0.3.1...v0.3.3

**Full Changelog**: https://github.com/Lexi-BU/lexi/compare/v0.3.0...v0.3.2

**Full Changelog**: https://github.com/Lexi-BU/lexi/compare/v0.3.0...v0.3.1

Major change:

Since a package by the name `lexi` already exists on [PyPi](https://pypi.org/project/lexi/), I decided to refactor the code so that we renamed the main folder of LEXI to `lexi_bu` (earlier it was simply `lexi`.

The latest version of `lexi` is available to be installed from PyPi at the following location: https://pypi.org/project/lexi-bu/

**Full Changelog**: https://github.com/Lexi-BU/lexi/compare/v0.2.0...v0.3.0

What's Changed

Description of all the modifications

1. Added unittest for most of the functions that are present in the `lexi` code.
2. The `array_to_image_kwargs` default value was assigned as `None` which would give error in the case where `array_to_image_kwargs` wasn't provided by the user. So, we modified it so that `array_to_image_kwargs` defaults to an empty dictionary instead of `None`.
3. Modified the `validate_input`, so that when one tries to validate `time_range`, with it being either `datetime`, `number` or a mix of it, the `time_range` is still validated.
4. Updated different functions, so that now `time_range` is appropriately validated and the values inside `time_range` is modified so that the final type of each element of `time_range` is a datetime object with `UTC` as a time-zone.
5. Modified `__init__.py` file:
a) Changed from `pkg_resources` to `importlib.metadata``
b) Added:

from .lexi import (
validate_input,
download_files_from_github,
get_lexi_data,
get_spc_prams,
get_exposure_maps,
get_sky_backgrounds,
get_lexi_images,
array_to_image,
)

6. Modified `lexi.py`:
a) Removed:

from lexi import __version__, __doc__

Add the docstring to the package
__doc__ = __doc__

Add the version to the package
__version__ = __version__

to avoid circular import error.

* 82 add unittests by qudsiramiz in https://github.com/Lexi-BU/lexi/pull/84


**Full Changelog**: https://github.com/Lexi-BU/lexi/compare/v0.1.0...v0.2.0