Version 2.6.4

Changes

• allow compacting of signed integers when appending
  • use the package function enable_integer_compacting
• avoid unnecessary computation for polynomial conversions
• add MLSD channel support
• improve plotting of maps and update Signal usage example
• moved __version__ to version.py

Fixes

• fix errors in HDF5 export
• fix error in get for singed integers of nonstandard size
• fix mask error for nonstandard integers
• fix error in MDF4 get method when channel type was virtual master