Implement a RAW file reader

Description

From the commit message:

The reader class reads one event at a time from a RAW file. The reader is able to automatically detect if the file is uncompressed or ZSTD compressed. In the later case, it is decompressed on the fly.

Related Issue

One step of many in #200 (closed).

How Has This Been Tested?

Test files can be read and unpacked by a modified version of !261 (merged). The end-of-file conditions is properly handled.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.