yatsm: Yet Another Time Series Model (YATSM): v0.6.1

Bug fix release and beginning of v0.6.x maintenance branch.

Version v0.6.x will be backward patched for any bug fixes (for an undetermined amount of time) as version v0.7.0 will introduce backwards incompatible changes in order to enable incorporation of data from multiple sensors and to better link time series models together in a cohesive pipeline.

• CCDCesque: Fixed case in which bands not used as "test indices" would not have time series models estimated (i.e., no coef or rmse) if the time series ends immediately after training #88
• RLM: Fixed divide by zero error when n == p (number of observations equals number of parameters estimated) #88