'pip install --upgrade xym' to keep xym up-to-date

[bclaise]

'pip install --upgrade xym' => doesn't contain the latest updates.

It turns out that the xym code in the github repository will extract the
modules from RFC8040 correctly; it's just that there's been no pip install release
since the necessary patch was applied in July 2016

Background:
The current toolchain runs xym to extract modules from new RFCs every
night. When processing RFC8040, xym reports:
{{{
ERROR: '/www/tools.ietf.org/rfc/rfc8040.txt', Line 4385 - Yang file not
specified in
ERROR: '/www/tools.ietf.org/rfc/rfc8040.txt', Line 4678 - 'module'
statement within another module
Created the following models:
example-ops.yang
example-actions.yang
example-mod.yang
}}}
which would explain why there's no ietf-restconf module from RFC8040
available ...

[bclaise]

pip package created for version 0.4