improve foramtting of _oasis

* align things better
* get rid of tabs
oasis digest update
added some sexp printing to explain failure
Merge pull request #159 from rgrinberg/master

Fix oasis formatting + add a couple of printers to tests
Update CHANGES for bin/cohttp_server_* improvements
cohttp_server: fix error handling

Now, ENOENT -> 404 and the async version responds with error codes. Also, fixed logging of requests which cause errors and printing of strange files. 404 doesn't leak local file paths, now (and isn't 500).
Update CHANGES for bin/cohttp_server_* improvements
fixes failing test

return Done instead of Chunk "" when nothing is read
Merge pull request #160 from rgrinberg/fix_tests

fixes failing test
Merge pull request #158 from dsheets/bin_cohttp_server

Improve bin/cohttp_server_*
bin/cohttp_server: index files should be served directly, not redirected
Merge pull request #162 from dsheets/bin_cohttp_server

bin/cohttp_server: index files should be served directly, not redirected
bin/cohttp_server: redirect bare directories to their slashed counterpart

Not a requirement or even a good idea... just conformance with common
servers. `dir` and `dir/` should almost certainly be collapsed but `dir`
-> `dir/` is common and `dir/` -> `dir` isn't (but is more aesthetic).
Merge pull request #164 from dsheets/bin_cohttp_server

bin/cohttp_server: redirect bare directories to their slashed counterpart
Always percent-decode paths before file system resolution. Fixes #157.
bin/cohttp_server: redirect to trailing slashes on auto-indexed directories, too
Clarify how resolution has changed
Merge pull request #165 from dsheets/bin_cohttp_server

Always percent-decode paths before file system resolution. Fixes #157.