v1.3.6

DoubleFloats v1.3.6

Diff since v1.3.5

Merged pull requests:

• fix subnormal sqrt and cbrt (#167) (@t-bltg)

Closed issues:

• invalid sqrt and cbrt result on subnormal numbers (#166)
• incorrect square function (#188)
• Is matrix multiplication multi-threaded for Double64? (#192)
• Is matrix multiplication multi-threaded for Double64? (#193)