v0.7.61

ApproxFunBase v0.7.61

Diff since v0.7.60

Merged pull requests:

• Tuple recursion in KroneckerOperator banded checks (#343) (@jishnub)
• Specialize isdiag for KroneckerOperator (#344) (@jishnub)
• Use isbanded from BandedMatrices (#345) (@jishnub)
• Version bump to v0.7.61 (#346) (@jishnub)