Minor fixes
This MR includes the following features:
- Makes it explicit the conversion to RGB images in image pre-processing pipelines
- Adds a transform for converting between 16-bit and 8-bit PNG images
- Allows the inferencer to work with globs instead of fixed paths (+ adaptations to this where needed)
- Adds documentation for
imagefolderinference
- Adds explicit dependence to bob.core, required by the 16/8 bit PNG converters
- Fixes an issue related to the conda recipe (see bob/bob.devtools#44 (closed) and bob/bob.devtools!127 (merged))