Enable the use of EMCEE 3 and PTEMCEE
This includes the possibility of using EMCEE 3 as well as PTEMCEE (including its dynamic temperature feature). The documentation is updated accordingly, as is the version number. Retrocompatibility with EMCEE 2 is still preserved. The version numbers of EMCEE and PTEMCEE are now included in the output README files.
Other improvements include:
- a different scaling of surface correction recipes - this leads to larger values of the amplitude coefficients, more comparable with other parameters
- various bug/deprecation fixes