Add category to library.properties
Add category to library.properties

Because no category is specified Arduino IDE 1.6.6 displays the warning:
`WARNING: Category '' in libraryFastCRC is not valid. Setting to 'Uncategorized'`
Every time any sketch is compiled, even if it doesn't include FastCRC.
FrankBoesing/FastCRC,FrankBoesing/FastCRC