Added configuration file.

The "default_content_type" option can be set to "form".

Closes #91.

httpie/config.py

@@ -1,8 +1,78 @@
 import os
+import json
+import errno
+
+from . import __version__
 from requests.compat import  is_windows
 
-__author__ = 'jakub'
+
+DEFAULT_CONFIG_DIR = (os.path.expanduser('~/.httpie')
+                      if not is_windows else
+                      os.path.expandvars(r'%APPDATA%\\httpie'))
 
 
-CONFIG_DIR = (os.path.expanduser('~/.httpie') if not is_windows else
-              os.path.expandvars(r'%APPDATA%\\httpie'))
+class BaseConfigDict(dict):
+
+    name = None
+    help = None
+
+    def __init__(self, directory=DEFAULT_CONFIG_DIR, seq=None, **kwargs):
+        super(BaseConfigDict, self).__init__(seq or [], **kwargs)
+        self.directory = directory
+
+    def __getattr__(self, item):
+        return self[item]
+
+    @property
+    def path(self):
+        try:
+            os.makedirs(self.directory, mode=0o700)
+        except OSError as e:
+            if e.errno != errno.EEXIST:
+                raise
+        return os.path.join(self.directory, self.name + '.json')
+
+    @property
+    def is_new(self):
+        return not os.path.exists(self.path)
+
+    def load(self):
+        try:
+            with open(self.path, 'rt') as f:
+                try:
+                    data = json.load(f)
+                except ValueError as e:
+                    raise ValueError(
+                        'Invalid %s JSON: %s [%s]' %
+                        (type(self).__name__, e.message, self.path)
+                    )
+                self.update(data)
+        except IOError as e:
+            if e.errno != errno.ENOENT:
+                raise
+
+    def save(self):
+        self['__version__'] = __version__
+        with open(self.path, 'w') as f:
+            json.dump(self, f, indent=4, sort_keys=True, ensure_ascii=True)
+            f.write('\n')
+
+    def delete(self):
+        try:
+            os.unlink(self.path)
+        except OSError as e:
+            if e.errno != errno.ENOENT:
+                raise
+
+
+class Config(BaseConfigDict):
+
+    name = 'config'
+
+    DEFAULTS = {
+        'default_content_type': 'json',
+    }
+
+    def __init__(self, seq=None, **kwargs):
+        super(Config, self).__init__(seq or [], **kwargs)
+        self.update(self.DEFAULTS)