Start writing Hesokuri database spec+design
Further iron out details of database format
Database design: add a way to specify which repos present on a peer

Also, clean up formatting and wording of the earlier section.
Database design: Add a clarification about using '/' in the path names
Utility code for reading Git tree objects
Use a Hash protocol with proper equality semantics

Stop using byte arrays and use a Hash protocol, implemented by ArrayBackedHash.
Use less confusing names for some identifiers

s/read-to/read-until/ for clarity
s/delim/term/ because "delimiter" seems to suggest a separator in a list, while
terminator suggests the final character
Add unit test for hesokuri.util/read-until
Add unit tests for Git hash and Git tree utility functions
Merge branch 'git-tree-and-hash-utility'