Rework eve_proxy to remove dependancy on eve_api and allow it to handle downtime situations better

eve_proxy/exceptions.py

@@ -0,0 +1,17 @@
+class DocumentRetrievalError(Exception):
+    """
+    Unable to retrieve a document from the EVE API: %s
+    """
+    def __init__(self, value):
+        self.value = value
+
+    def __str__(self):
+        return self.__doc_ % value_
+
+class InvalidDocument(Exception):
+    """
+    The document retrieved from the EVE API is not a valid XML document
+    """
+    def __str__(self):
+        return self.__doc__
+