[Proj] Moving Math Constants to projects.h

[Micah Cochran]

I've submitted a pull request to move math constants (most are some version
of PI) that have been used multiple places into projects.h.
https://github.com/OSGeo/proj.4/pull/372

Also, I've renamed a few of the less obvious constants names to more
obvious names.  I've added psuedocode for the constants (example FORTPI is
pi/4).  I've did some extra testing (beyond Travis-CI test) to make fairly
sure that any changes that I made did not alter the algorithms.  I would be
willing to add those test to proj.4.


Please let me know if there are any issues.


Thank you,
-- 

*Micah Cochran*

GIS Coordinator  -  City of Athens  -  Engineering Services & Community
Development Dept.  -  Dept. of Public Works Building  -  1600 ELM ST W,
Athens, AL <http://g.co/maps/ncrp7> - geo:34.820608,-86.991474 -  p.
256-233-2224  -  f. 256-233-8791 - www.athensalabama.us
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