yaml config file option added
fixed #1
added invalid certificate message
version 1.0.0.pre.4
adding code to read cert from file
assume that the certificate files are in the same directory as the yaml config file
adding external_id to message to_json
moving ext id to Core
Merge pull request #3 from tilo/feature/tracking-external-ids

adding external_id to message to_json
Merge pull request #2 from tilo/feature/yaml-adding-certificate-reading

adding reading of certificates from file