v0.20.6

Optim v0.20.6

Diff since v0.20.5

Closed issues:

• Gradients not working correctly with Double64 type from DoubleFloats (#761)
• Unused return value from update_state!() in optimize() (#789)
• brent returns spurious minimum (#798)
• It seems like dot is being incorrectly overwritten (#801)

Merged pull requests:

• Update the documentation of the callback function. (#795) (@hcarlsso)
• fix Brent for flat functions (#799) (@bjarthur)
• Fix typo in IPNewton docs (#800) (@rcurtin)