Instructions in INSTALL.md are out of date

[odellus]

I was following along the instructions to install, so I downloaded OCC 7.5.2 as it says in INSTALL.md. Then when I go to build pythonocc-core, I see

CMake Error at CMakeLists.txt:151 (find_package):
  Could not find a configuration file for package "OpenCASCADE" that is
  compatible with requested version "7.5.3".

  The following configuration files were considered but not accepted:

    /usr/local/lib/cmake/opencascade/OpenCASCADEConfig.cmake, version: 7.5.2
    /home/thomas/Downloads/occt-0dc2c37/cmake-build/OpenCASCADEConfig.cmake, version: 7.5.2

So I created a PR ( #1106 ) to try to update the instructions in INSTALL.md. I bumped the build version and changed the download URL to get OCC 7.5.3. It took me a really long time to build OCC so I'll report back probably sometime tomorrow if the simple fix I propose in #1106 is sufficient.

[odellus]

Needed this gem to figure out I needed to write a python script to uninstall OCC before reinstalling to prevent getting this error.

CMake Error at CMakeLists.txt:917 (file):
  file failed to open for writing (Permission denied):

    /usr/local/bin/custom.sh

# filename: uninstall.py
import os
with open('install_manifest.txt','r') as f:
    installed = f.read().split('\n')
for fname in installed:
    if os.path.exists(fname):
        os.remove(fname)

then sudo python uninstall.py in the 7.5.2 cmake-build directory where the install manifest lives.