Version 2.2.0

This release included the following updates from pull requests:

• Bug fix for DataCollection where names is None (#62).
• Added detector propagation to rebin and resample (#65).
• Added functions to create FITS headers with floating-point values (#69).
• Updated calls to matplotlib and fixed some headers (#71).
• Renamed exponential_card to scientific_card and added some options (#72).
• Reduced polygon artifacts for maps with fragmented contours (#77).
• Fixed creating and plotting effective area on the sky (#81).
• Fixed 'Pha.energy_range' when creating from Phaii.to_pha() (#82).
• Improved the creation of PHA objects with 'valid_channels' (#83).
• Removed the need for using a FILENAME in the header of a PHA file (#84).
• Added translation function to Range (#85).
• Fixed more calls to matplotlib (#86).
• Added support for trigger detection (#90).