Introduce error 2000

Adds separate type of errors to use when the client sent a valid XML that does not include a valid command element.

Ensure that session_id is always present

Merge pull request #16 from internetee/fix-missing-state

Ensure that state has always a session_id

Log SSL handshake errors

Add additional logging facility for TLS errors, so we'd know which client they come from.

Update documentation on release process

No functional changes.

Test deployment release

v0.1.6

Fix readme

Add appup.src

v0.1.5

Create appup.src file (#12)

Relup

Include rebar3 plugins for relups

Include frame parameter

Include frame parameter in requests that are sent to registry. Resolves a compatibility issue with old mod_epp.