update to new API
respect server-reported stretching parameters
demo-client.py: factor out stretching
demo-client.py: factor out mainKDF
demo-client.py: add password-change. Doesn't work yet.
add "make help" with some instructions
demo-client.py: changepw works, with server patch
demo-client.py: add destroy
demo-client: start on forgot-password, not complete
make help: mention 'destroy account'
anticipate different constraints on the test vectors
add alternative constraints: leading 0x00 bytes in x/M1/K/u
add mode switch (argv[1])
use keyRequestKey in account/keys
disabled code to print vectors in a JS-friendly format
update URL handling: versioning, use 127.0.0.1 not "localhost"

Using "localhost" when the server expects to be known as "127.0.0.1"
produces incorrect HAWK headers. All endpoints except "__heartbeat__"
have a "/v1" prefix in their URLs.
remove bug workaround (hex-encoded HAWK keys)

the current version of the server no longer suffers from this bug
add (disabled) code to mangle email/srpPW to match picl-gherkin bug

https://github.com/mozilla/picl-gherkin/issues/33 covers a bug in the JS
client library which incorrectly performs double-encoding of the account
email address and the derived srpPW fields. This results in
accounts (srpVerifier and unwrapBkey) that don't match the spec,
breaking interoperability with other (compliant) implementations.

By turning on "MANGLE=True" on line 198, this code will match the buggy
behavior of picl-gherkin, enabling temporary interoperability.

We are changing picl-gherkin to match the spec, of course, not the other
way around.