Mention SimpleXML and JSON extension requirements in the README.
Add lib/autoload.php to allow manual (i.e. without composer) installation.

The custom autoloader created by this commit translates class
names into filesystem locations by a simple rule: it replaces
backslashes with frontslashes, and adds ".php" on the end. Two
locations are searched for this class implementation file: first we
check under lib/, then under test/.

The existing test/bootstrap.php checked for vendor/autoload.php and
would show an error to the user if it did not exist. Now that we have
our own autoloader, we can just use that instead. So, test/bootstrap.php
was removed, and phpunit.xml.dist was pointed at the new lib/autoload.php
for its bootstrap code.

Thanks to Artur Weigandt for the implementation of the autoloader.
Use consistent indentation in bullet lists.
Add documentation for the manual installation method to the README.
Update the PHP version requirement in the README per composer.json.
Add requirements/instructions for running the test suite to the README.
Reduce bullet indentation one level in the README.
Whitespace fixes in lib/autoload.php.

* Use four spaces for indentation of "if" statements.
* Add a space between parenthesis and braces, e.g. if (foo) {...
* Remove spaces around the string concatenation operator (dot). This
  is consistent with its usage in Redmine/Client.php.
Merge pull request #96 from orlitzky/master

Add autoloader to allow manual installation and update documentation