### Summary
Closes#1018. Enables `partition_email` and `partition_msg` to detect if
an email has PGP encrypted content. Based on the specification in [RFC
2015](https://www.ietf.org/rfc/rfc2015.txt). The test emails are based
on the example email in the spec. If PGP detected content is detected, a
warning is emitted and an empty set of lists is returned.
### Testing
```python
from unstructured.partition_email import partition_email
filename = "example-docs/eml/fake-encrypted.eml"
partition_email(filename=filename)
```
```python
from unstructured.partition_msg import partition_msg
filename = "example-docs/fake-encrypted.msg"
partition_msgl(filename=filename)
```
### Summary
Closes#1007. Adds a deprecation warning for the `file_filename` kwarg
to `partition`, `partition_via_api`, and `partition_multiple_via_api`.
Also catches a warning in `ebooklib` that we do not want to emit in
`unstructured`.
### Testing
```python
from unstructured.partition.auto import partition
filename = "example-docs/winter-sports.epub"
# Should not emit a warning
with open(filename, "rb") as f:
elements = partition(file=f, metadata_filename="test.epub")
# Should be test.epub
elements[0].metadata.filename
# Should emit a warning
with open(filename, "rb") as f:
elements = partition(file=f, file_filename="test.epub")
# Should be test.epub
elements[0].metadata.filename
# Should raise an error
with open(filename, "rb") as f:
elements = partition(file=f, metadata_filename="test.epub", file_filename="test.epub")
```
Documentation Overhaul
- Added documentation hierarchy
- Added options for Bash vs Python for API & Upstream Connectors
- Added Introduction section (Overview, Key Concepts, Getting Started)
- Redid connectors section
- Installation is now broken up (needs further work)
