Implements spike check
Ensure low threshold less than high threshold
Take previously set QC flags into account
Added tests for previous QC values
Refactor assignment to take place on one line
Merge pull request #12 from benjwadams/add_qual_flags

Take previously set QC flags into account
Change PrimaryFlags to SecondaryFlags
Use numpy.testing functions in tests
Revert "Change PrimaryFlags to SecondaryFlags"

This reverts commit 4cce6cf9ca497c7f77a464e21a9ec423c48d112a.
Merge pull request #9 from benjwadams/spike_check_fix

Spike check implementation