Add likelihood comparison against phyml

[johnlees]

TODO:

• [x] Verify it actually works (currently the values are different)
• [x] Add phyml to the CI so this can be run on github

[johnlees]

phyml: -172679.947211691149277612567 bactree: -599832.4882322458

[johnlees]

NB: renaming from maple to bactree (for now at least)