Drop Python 3.6 support from Windows installer

Python 3.6 is well past end of life, and we now
build and test with 3.9, so drop it from the installer.

ChangeLog.md

@@ -4,7 +4,7 @@ ChangeLog {#changelog}
 # HEAD
 - We no longer provide packages for Ubuntu 18.04 LTS (Bionic Beaver), as it
   reached end of life in May 2023.
-- The Windows .exe installer now supports Python 3.12.
+- The Windows .exe installer now supports Python 3.7 through 3.12.
 
 # 2.19.0 - 2023-06-22 # {#changelog_2_19_0}
 - Most IMP Value and Object types can now be serialized (or pickled in Python).

tools/w32/make-package.sh

@@ -11,7 +11,7 @@
 # make DESTDIR=`pwd`/w32-inst install
 #
 # Where $w32py is the path containing Python headers and libraries.
-# Repeat for all desired Python versions (3.6, 3.7, 3.8, 3.9, 3.10, 3.11,
+# Repeat for all desired Python versions (3.7, 3.8, 3.9, 3.10, 3.11,
 # and 3.12 for us)
 #
 # Then run (still in the binary directory)
@@ -89,7 +89,7 @@ for app in ${ROOT}/bin/*; do
 done
 
 # Make Python version-specific directories for extensions (.pyd)
-PYVERS="3.6 3.7 3.8 3.9 3.10 3.11 3.12"
+PYVERS="3.7 3.8 3.9 3.10 3.11 3.12"
 for PYVER in ${PYVERS}; do
   mkdir ${ROOT}/python/python${PYVER} || exit 1
   mkdir ${ROOT}/python/python${PYVER}/_ihm_pyd || exit 1

tools/w32/pkg-README.txt

@@ -4,7 +4,7 @@ so can be run simply by opening a Command Prompt, changing to this bin
 directory (or adding it to your PATH), and typing 'foxs'.
 
 The IMP Python libraries are automatically set up to work with any version of
-Python 3 from 3.6 to 3.12. (You need to download Python separately from
+Python 3 from 3.7 to 3.12. (You need to download Python separately from
 www.python.org and install it; be sure to get the 64-bit version of Python
 if you installed the 64-bit version of IMP, and likewise for the 32-bit
 version - you can't mix and match.)

tools/w32/w32-install.nsi

@@ -81,7 +81,6 @@ Section ""
   WriteRegDWORD HKLM "${UNINST_KEY}" "NoModify" 1
   WriteRegDWORD HKLM "${UNINST_KEY}" "NoRepair" 1
 
-  WriteRegStr HKLM "Software\Python\PythonCore\3.6${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}" "" "$INSTDIR\python"
   WriteRegStr HKLM "Software\Python\PythonCore\3.7${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}" "" "$INSTDIR\python"
   WriteRegStr HKLM "Software\Python\PythonCore\3.8${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}" "" "$INSTDIR\python"
   WriteRegStr HKLM "Software\Python\PythonCore\3.9${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}" "" "$INSTDIR\python"
@@ -116,7 +115,6 @@ Section "Uninstall"
 
   DeleteRegKey /ifempty HKLM "Software\${PRODVER}"
   DeleteRegKey HKLM "${UNINST_KEY}"
-  DeleteRegKey HKLM "Software\Python\PythonCore\3.6${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}"
   DeleteRegKey HKLM "Software\Python\PythonCore\3.7${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}"
   DeleteRegKey HKLM "Software\Python\PythonCore\3.8${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}"
   DeleteRegKey HKLM "Software\Python\PythonCore\3.9${PYTHON_ARCH_SUFFIX}\PythonPath\${PRODVER}"