0.29.3

Features:

• debug_images is now a default feature. (#545
• Added a from_path_raw function to Envelope that reads an envelope from a file without parsing anything. (#549)
• Added a data method to performance::Span that gives access to the span's attached data. (#548)

Fixes:

• Envelopes will be discarded rather than blocking if the transport channel fills up. (#546)