ENH Educated guess of NSS loading based on bitness

If Python's bitness doesn't match that of the NSS.dll found,
loading will fail. This restricts directories on a 64bit Windows system.
A better solution would check the bitness of the lib as well - refs #41

CHANGELOG.md

@@ -7,6 +7,7 @@
 - Using `--pass-prefix=''` prevents creation of a prefix: `web/address/...` becomes `address/...`
 - Fix an encoding bug due to non-ASCII characters leading to a user's profile path
 - Drop support for Python 2 on Windows. Python 3 works fine.
+- Explicitly target 32/64bit Mozilla folders depending on Python bitness
 
 ##### 0.7.0
 - Fix PK11 slot memory leak

firefox_decrypt.py

@@ -54,6 +54,7 @@ except ImportError:
 PY3 = sys.version_info.major > 2
 LOG = None
 VERBOSE = False
+SYS64 = sys.maxsize > 2**32
 
 if not PY3 and os.name == "nt":
     sys.stderr.write("WARNING: You are using Python 2 on Windows. If your "
@@ -342,11 +343,22 @@ class NSSDecoder(object):
         """
         if os.name == "nt":
             nssname = "nss3.dll"
+            if SYS64:
+                locations = (
+                    "",  # Current directory or system lib finder
+                    r"C:\Program Files\Mozilla Firefox",
+                    r"C:\Program Files\Mozilla Thunderbird",
+                    r"C:\Program Files\Nightly",
+                )
+            else:
                 locations = (
                     "",  # Current directory or system lib finder
                     r"C:\Program Files (x86)\Mozilla Firefox",
-                r"C:\Program Files\Mozilla Firefox",
+                    r"C:\Program Files (x86)\Mozilla Thunderbird",
                     r"C:\Program Files (x86)\Nightly",
+                    # On windows 32bit these folders can also be 32bit
+                    r"C:\Program Files\Mozilla Firefox",
+                    r"C:\Program Files\Mozilla Thunderbird",
                     r"C:\Program Files\Nightly",
                 )
 
@@ -371,13 +383,27 @@ class NSSDecoder(object):
 
         else:
             nssname = "libnss3.so"
+            if SYS64:
+                locations = (
+                    "",  # Current directory or system lib finder
+                    "/usr/lib64",
+                    "/usr/lib64/nss",
+                    "/usr/lib",
+                    "/usr/lib/nss",
+                    "/usr/local/lib",
+                    "/usr/local/lib/nss",
+                    "/opt/local/lib",
+                    "/opt/local/lib/nss",
+                    os.path.expanduser("~/.nix-profile/lib"),
+                )
+            else:
                 locations = (
                     "",  # Current directory or system lib finder
                     "/usr/lib",
-                "/usr/lib32",
-                "/usr/lib64",
                     "/usr/lib/nss",
+                    "/usr/lib32",
                     "/usr/lib32/nss",
+                    "/usr/lib64",
                     "/usr/lib64/nss",
                     "/usr/local/lib",
                     "/usr/local/lib/nss",