merge: add basic library tests

Add tests for:
- attach    functions
- base64    functions
- body      functions
- buffer    functions
- charset   functions
- date      functions
- email     functions
- envelope  functions
- envlist   functions
- file      functions
- from      functions
- hash      functions
- history   functions
- list      functions
- logging   functions
- mapping   functions
- mbyte     functions
- md5       functions
- memory    functions
- parameter functions
- parse     functions
- regex     functions
- rfc2047   functions
- rfc2231   functions
- sha1      functions
- signal    functions
- tags      functions
- thread    functions
- url       functions