Add sinh stretch option to simple_norm

[larrybradley]

Description

This PR adds a sinh stretch option to simple_norm, which already has the inverse asinh stretch.

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[pllim]

LGTM but does this need a What's New entry?

[pllim]

p.s. Appears to have a conflict.

[larrybradley]

@pllim I don't think this is a big enough addition for a "What's New" entry.

[pllim]

Thanks!