Release Candidate: v0.3rc2

Various small fixes over 0.3rc1:

• fix #35 - CLI still using previous API
• fix #36 - whitespace error breaking chopping
• start adding matplotlib fallback plotting
• document Metric class
• add gui class docstrings
• gracefully handle missing extrae ON/OFF events
• include progresswidgets within gui
• small code quality fixups
• fix resource_filename warnings
• further improve scaling plot rendering
• Further update scaling plot colors
• fix broken scaling plot title
• add initial good/bad shading support to plots
• add frequency scaling metric
• Added -S 32k flag to Dimemas call
• Fixed histogram maximum and delta
• fix png saving for cli