Allowing variable length records

[hattesen]

For logging purposes, it would be a great improvement, if the library would be able to support variable length messages. Possibly by linking multiple (short) fixed length messages, or allowing a struct and a variable length string to be stored (with a pascal-style string length).

I may fork and attempt an implementation myself, and then create a pull-request back.

Any pointers as to how this may be achieved in a low-impact, yet safe/secure way?