* **FEATURE:** added a `write` method to the `_base_recipe` to write frames to disk (renames extensions to ESO preferred naming scheme)
* **FEATURE:** detector lookup class added alongside yaml files to host detector specific parameters (rotation, science-pixels etc). Code has been updated to remove hard-wired detector values.
* **FEATURE:** added a cleanup method to remove intermediate file once recipe completes
* **ENHANCEMENT:** parameters for clip and stack method added to the settings files
* **ENHANCEMENT:** added strict typing of data and variables with astropy units to avoid silent mistakes in frame arithmetic
* **ENHANCEMENT:** added mixing of readout speeds to input frame verification checks
* **ENHANCEMENT:** added readnoise and gain to the list of keyword values to check during frame verification
* **ENHANCEMENT:** inject a 'SOXSPIPE PRE' keyword with timestamp value into prepared frames
* **ENHANCEMENT:** check frames for 'SOXSPIPE PRE' keyword before preparing - raises exception if found
* **ENHANCEMENT:** ron and gain are added to the recipe's detector lookup dictionary during frame verification (so they don't need read again later)
* **REFACTOR:** moved stacking code to it own `clip_and_stack` method hosted in the `_base_recipe`
* **REFACTOR:** moved basic input frame verifications to the `_base_recipe` - so not to repeat code
* **REFACTOR:** removed python 2.7 support - not feasible with CCDProc
* **DOCS:** added workflow diagrams to the documentation for many of the methods implemented (`prepare_frames()`, ``clip_and_stack``)