SRFI 69, 125, 126: hash-tables

[lassik]

Here are all the hash-table APIs I'm aware of:

• SRFI 69: Basic hash tables
• SRFI 125: Intermediate hash tables
• SRFI 126: R6RS-based hashtables

Would be nice to supply all of these as wrappers around Gambit's native hash-tables. @feeley can you estimate whether there are any roadblocks? If not, I can start working on them in the near future.

Vyzo said on the mailing list that Gerbil has 125 using Gambit's hash-tables. AFAICT 125 is a super-set of 69.

[lassik]

SRFI 69 is already in Gambit's main repo: lib/srfi/69

@feeley Should we add the 125 and 126 wrappers right into the main repo as well? Since they are so similar to 69, it might be easier than developing them here separately.