v0.1.21

ITensors v0.1.21

Diff since v0.1.20

Closed issues:

• Try to make ITensors.jl compatible with earlier Julia versions (#398)

Merged pull requests:

• Add parity conservation to S=1/2 sitetype (#467) (@mtfishman)
• Add ! as not syntax (#471) (@mtfishman)
• Add Sweeps constructor from matrix of parameters (#472) (@mtfishman)
• Add examples of input files (#473) (@mtfishman)