v0.5.0

• Large refactor of training code
  • Resolve hanging at the end of training #15
  • Switch to CuDNN for GRU layers
  • Improved storage and retrieval of features for better IO
  • Training speed improved >10X
• Resolve issue with contained chunks during stitching #20
• Changes to medaka_consensus
  • checks presence of minimap2 and samtools
  • provides more feedback on error #16