Add a pure-python version of the Black-Scholes function for comparison with the Cython equivalent
Add a pure-python version of the Black-Scholes function for comparison with the Cython equivalent

fabianrost84/cython,JelleZijlstra/cython,slonik-az/cython,fperez/cython,c-blake/cython,c-blake/cython,fabianrost84/cython,mrGeen/cython,mcanthony/cython,cython/cython,dahebolangkuan/cython,mrGeen/cython,achernet/cython,encukou/cython,mcanthony/cython,hickford/cython,slonik-az/cython,acrispin/cython,slonik-az/cython,hickford/cython,achernet/cython,JelleZijlstra/cython,roxyboy/cython,hhsprings/cython,hickford/cython,dahebolangkuan/cython,mcanthony/cython,andreasvc/cython,acrispin/cython,madjar/cython,da-woods/cython,roxyboy/cython,ABcDexter/cython,achernet/cython,da-woods/cython,mrGeen/cython,c-blake/cython,hhsprings/cython,da-woods/cython,dahebolangkuan/cython,roxyboy/cython,fabianrost84/cython,scoder/cython,ABcDexter/cython,marscher/cython,fperez/cython,cython/cython,achernet/cython,scoder/cython,cython/cython,scoder/cython,fabianrost84/cython,acrispin/cython,marscher/cython,acrispin/cython,encukou/cython,da-woods/cython,ChristopherHogan/cython,madjar/cython,JelleZijlstra/cython,madjar/cython,ABcDexter/cython,encukou/cython,slonik-az/cython,madjar/cython,hhsprings/cython,marscher/cython,mrGeen/cython,ABcDexter/cython,andreasvc/cython,marscher/cython,mrGeen/cython,achernet/cython,dahebolangkuan/cython,fperez/cython,hhsprings/cython,scoder/cython,ChristopherHogan/cython,encukou/cython,madjar/cython,mcanthony/cython,c-blake/cython,cython/cython,dahebolangkuan/cython,mcanthony/cython,fperez/cython,roxyboy/cython,andreasvc/cython,ChristopherHogan/cython,slonik-az/cython,andreasvc/cython,JelleZijlstra/cython,fabianrost84/cython,hickford/cython,hickford/cython,fperez/cython,andreasvc/cython,ABcDexter/cython,c-blake/cython,hhsprings/cython,JelleZijlstra/cython,encukou/cython,roxyboy/cython,acrispin/cython,marscher/cython