Acefile

- Rephrase setup failure notices for clarity.
- Improve seekable conformance of internal file-like wrappers.
- Minor maintainability and test improvements.

- Fix an IndexError exception while decompressing corrupt archives, that also
manifested for some encrypted ACE archives when using a wrong password
(bug reported by Jonathan Leonard).
- Parse all variants of recovery headers for dumping and diagnostics, but
still ignore the actual recovery data (issue 11).
- Expose the `--debug` option in the CLI usage information and make its
output slightly more understandable.

- Add unit test for WinRAR/unacev2.dll vulnerability CVE-2018-20250 to
ensure and verify that acefile is not vulnerable.
- Migrate to new PGP key 0xE1520675375F5E35 for release signing.

- Fix reading archives from stdin in CLI on Windows.

- Substantially improve filename sanitization to avoid absolute path
overwrites, filenames containing reserved characters or matching reserved
names.

- Fix build of c extension on platforms without C99 support enabled by
default (pull req 12, joesecurity).