Fix dependencies

Merge pull request #10 from mpmiszczyk/feature/build-fix

Fix dependency on working wsock/wsecli instead of depending on breaking master

Use exml 2.1.0

2.3.1

Mark escalus_stanza.erl as using integer_to_binary/1

Standalone XMPP client

• allow to use Escalus as a standalone XMPP client
• add binary_to_integer/integer_to_binary workaround for older Erlang releases
• improve logging and XMPP stanzas dump in case of error
• improve interoperability with ejabberd (in case of rpc calls)
• support SCRAM-SHA1 authentication