v0.4.0

FLOWMath v0.4.0

Diff since v0.3.3

Merged pull requests:

• Make FLOWMath.brent complex-step safe (#18) (@dingraha)
• add second derivative function and matching test for akima splines (#19) (@juddmehr)
• add smoothing methods for more than two functions (#20) (@taylormcd)
• expose eps parameter in Akima spline construction (#21) (@tylercritchfield)
• Interp doc update (#22) (@juddmehr)
• bump version @JuliaRegistrator register (#23) (@juddmehr)