Replace MD5Digest with a more sane implementation

Means that all bytecode tests had to be updated; we replace all 16 characters of
the dump with "X" before testing. One test still depends on ordering though.

The old implementation used MD5 and an ill-shaped, illegal Base64 encoding; the
new implementation uses SHA1 and Base32hex encoding provided by Guava.
Update release notes
Hashing: implement, and use, a Funnel for a (list of) ASM Labels
Rename LabelFunnel to LabelListFunnel
Add a Funnel for an ASM FieldNode