Parametric curves support

[adam-urbanczyk]

This will resolve #91 . Also in principle #37 could be solved by this PR.

Sneak preview of the functionality:

import cadquery as cq
from math import sin, cos,pi,floor

def hypocycloid(t,r1,r2):
    return ((r1-r2)*cos(t)+r2*cos(r1/r2*t-t),(r1-r2)*sin(t)+r2*sin(-(r1/r2*t-t)))

def epicycloid(t,r1,r2):
    return ((r1+r2)*cos(t)-r2*cos(r1/r2*t+t),(r1+r2)*sin(t)-r2*sin(r1/r2*t+t))

def gear(t,r1=2,r2=1):
    if (-1)**(1+floor(t/2/pi*(r1/r2))) < 0:
        return epicycloid(t,r1,r2)
    else:
        return hypocycloid(t,r1,r2)

result = cq.Workplane('XY').parametricCurve(lambda t: gear(t*2*pi,6,1)).twistExtrude(15,90)
show_object(result)

[codecov]

Codecov Report

Merging #110 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #110      +/-   ##
==========================================
+ Coverage   94.26%   94.29%   +0.02%     
==========================================
  Files          19       19              
  Lines        3922     3942      +20     
==========================================
+ Hits         3697     3717      +20     
  Misses        225      225

Impacted Files	Coverage Δ
tests/TestCadQuery.py	98.77% <ø> (+0.01%)	⬆️
cadquery/cq.py	93.3% <100%> (+0.08%)	⬆️

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[adam-urbanczyk]

I think it is ready for review. I made quite some changes to the spline function so please take a good look.

I also added one example to the docs.

[jmwright]

Looks good. You're adding even more exiting functionality.

[dcowden]

+1 for this, looks great and adds hotness too.

[dcowden]

looks good to me

[adam-urbanczyk]

@dcowden +1 for hotness : ). Merging.