Replace xml-rs by quick_xml

quick_xml is way faster than xml-rs

Here is an example with a quick atom parser:
    With xml-rs:
        test parse_factorio_atom ... bench:   3,295,678 ns/iter (+/- 165,851)
    With quick_xml:
        test parse_factorio_atom ... bench:     203,215 ns/iter (+/- 13,485)

Unfortunately I had to break the API for this change to happen.
* Element::from_reader now takes `R: BufRead` instead of `R: Read`
* Element::write_to now takes `W: io::Write` instead of `EventWriter<W: Write>`

This migration also allow us to have a write_to function which assumes
we're already in a given namespace (see `write_to_in_namespace`).

src/error.rs

@@ -1,30 +1,30 @@
 //! Provides an error type for this crate.
 
-use std::io;
-
 use std::convert::From;
 
-use xml::writer::Error as WriterError;
-use xml::reader::Error as ReaderError;
-
 error_chain! {
     foreign_links {
-        XmlWriterError(WriterError)
-            /// An error with writing an XML event, from xml::writer::EventWriter.
+        XmlError(::quick_xml::errors::Error)
+            /// An error from quick_xml.
         ;
-        XmlReaderError(ReaderError)
-            /// An error with reading an XML event, from xml::reader::EventReader.
+        Utf8Error(::std::str::Utf8Error)
+            /// An UTF-8 conversion error.
         ;
-        IoError(io::Error)
+        IoError(::std::io::Error)
             /// An I/O error, from std::io.
         ;
     }
 
     errors {
-        /// En error which is returned when the end of the document was reached prematurely.
+        /// An error which is returned when the end of the document was reached prematurely.
         EndOfDocument {
             description("the end of the document has been reached prematurely")
             display("the end of the document has been reached prematurely")
         }
+        /// An error which is returned when an element is closed when it shouldn't be
+        InvalidElementClosed {
+            description("The XML is invalid, an element was wrongly closed")
+            display("the XML is invalid, an element was wrongly closed")
+        }
     }
 }