title: Making proj_api.h available for pip install cartopy
body: <p>I am trying to install <code>cartopy</code> via <code>pip install cartopy</code>. I have installed <code>proj.4</code> and it has placed a necessary file here</p>
  
  <p><code>
  ~/Downloads/proj-4.9.2 $ ls -l /usr/local/include/proj_api.h
  -rw-r--r--@ 1 dom  admin  5911 Nov 21 11:06 /usr/local/include/proj_api.h
  </code></p>
  
  <p>But <code>pip install</code> is not finding it:</p>
  
  <p><code>
      gcc -fno-strict-aliasing -I/Applications/SageMath/local/var/tmp/sage/build/python2-2.7.10.p2/include -DNDEBUG -g -fwrapv -O3 -Wall -Wno-unused -I/Applications/SageMath/local/include -I./lib/cartopy -I/usr/local/Cellar/geos/3.5.0/include -I/Applications/SageMath/local/include/python2.7 -c lib/cartopy/trace.cpp -o build/temp.macosx-10.9-x86_64-2.7/lib/cartopy/trace.o
      lib/cartopy/trace.cpp:282:22: fatal error: proj_api.h: No such file or directory
       #include "proj_api.h"
                            ^
      compilation terminated.
      error: command 'gcc' failed with exit status 1
  </code></p>
  
  <p>How do I get something like <code>-I/usr/local/include</code> to appear in the above <code>gcc</code> command? Somehow <code>-I/usr/local/Cellar/geos/3.5.0/include</code> gets put there.</p>