Added a pyinstaller spec file for building on windows.

This incorperates a work-around from here:
pyinstaller/pyinstaller#1966

This isn't perfect:

 - you need to modify your python directory on windows (copy
   c:/python27/lib/site-packages/gnome/shared to c:/python27/shared)

 - after generating the exe file, you also need to copy the glade file
   and the svg files into the dist dir, or the exe will crash.

This relates to issue #15.

I also updated the .gitignore file.

.gitignore

@@ -1,6 +1,9 @@
 *.nw
 *.png
 *.gif
+build/
+dist/
+*.zip
 sprites/
 out/
 *~

converter_gui.spec

@@ -0,0 +1,32 @@
+# -*- mode: python -*-
+
+import os
+import site
+
+block_cipher = None
+
+typelib_path = os.path.join(site.getsitepackages()[1], 'gnome', 'lib', 'girepository-1.0')
+
+a = Analysis(['converter_gui.py', 'converter_gui.spec'],
+             pathex=['C:\\Users\\Mym\\Downloads\\nw-converter'],
+             binaries=[(os.path.join(typelib_path, tl), 'gi_typelibs') for tl in os.listdir(typelib_path)],
+             datas=None,
+             hiddenimports=[],
+             hookspath=[],
+             runtime_hooks=[],
+             excludes=[],
+             win_no_prefer_redirects=False,
+             win_private_assemblies=False,
+             cipher=block_cipher)
+pyz = PYZ(a.pure, a.zipped_data,
+             cipher=block_cipher)
+exe = EXE(pyz,
+          a.scripts,
+          a.binaries,
+          a.zipfiles,
+          a.datas,
+          name='converter_gui',
+          debug=False,
+          strip=False,
+          upx=True,
+          console=True )