Do not automatically install windows-curses on Windows

It breaks installation with pip on MSYS2, and Kconfiglib can still be
useful without the terminal menuconfig.

Unfortunately, MSYS2 seems tricky to identify via environment markers
(https://www.python.org/dev/peps/pep-0508/#environment-markers).

This has breakage/annoyance potential, as windows-curses now needs to be
installed manually. The major Kconfiglib version will be increased.
Sorry if this change caused problems!

Fixes: #77

README.rst

@@ -126,9 +126,9 @@ Manual installation
 ~~~~~~~~~~~~~~~~~~~
 
 Just drop ``kconfiglib.py`` and the scripts you want somewhere. There are no
-third-party dependencies (except for the `windows-curses
-<https://github.com/zephyrproject-rtos/windows-curses>`_ package on Windows,
-when running the terminal ``menuconfig`` implementation).
+third-party dependencies, but the terminal ``menuconfig`` won't work on Windows
+unless a package like `windows-curses
+<https://github.com/zephyrproject-rtos/windows-curses>`_ is installed.
 
 Installation for the Linux kernel
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -507,9 +507,7 @@ Three configuration interfaces are currently available:
 
   There are no third-party dependencies on \*nix. On Windows,
   the ``curses`` modules is not available by default, but support
-  can be added by installing the ``windows-curses`` package (which is
-  installed automatically when Kconfiglib is installed via ``pip``
-  on Windows):
+  can be added by installing the ``windows-curses`` package:
 
   .. code-block:: shell
 

menuconfig.py

@@ -174,12 +174,11 @@
 Limitations
 ===========
 
-Doesn't work out of the box on Windows, but can be made to work with 'pip
-install windows-curses'. See the
-https://github.com/zephyrproject-rtos/windows-curses repository.
+Doesn't work out of the box on Windows, but can be made to work with
 
-'pip install kconfiglib' on Windows automatically installs windows-curses
-to make the menuconfig usable.
+    pip install windows-curses
+
+See the https://github.com/zephyrproject-rtos/windows-curses repository.
 """
 from __future__ import print_function
 

setup.py

@@ -61,12 +61,8 @@
         )
     },
 
-    # The terminal menuconfig implementation uses the standard Python 'curses'
-    # module. The windows-curses package makes it available on Windows. See
-    # https://github.com/zephyrproject-rtos/windows-curses.
-    install_requires=(
-        'windows-curses; sys_platform == "win32"',
-    ),
+    # Note: windows-curses is not automatically installed on Windows anymore,
+    # because it made Kconfiglib impossible to install on MSYS2 with pip
 
     # Needs support for unnumbered {} in format() and argparse
     python_requires=">=2.7,!=3.0.*,!=3.1.*",