patterns: add bcss (BeyondCompare SnapShot) file

[ttimasdf]

Pattern

BeyondCompare BCSS file is created by Snapshots feature of Beyond Compare software.

This format consists of a header and zlib-compressed content. Additional instructions and procedures were added to support both the file and its decompressed content.

Checklist

• A pattern for this format doesn't exist yet (or this PR improves the existing one)
• The new pattern has been added to the relevant table in the Readme
• The new pattern has a description pragma (#pragma description My pattern Description here)
• The pattern was associated with all relevant MIME types (using #pragma MIME mime-type in the source code)
  • Make sure to never use application/octet-stream here as that means "Unidentifiable binary data"
• A test file for this pattern has been added to /tests/patterns/test_data
  • Try to keep this file below ~ 1 MB

[WerWolv]

Thanks a lot! :)