v0.9.0

• Added: Introduced support for file downloads (see docs for details)
• Added: Introduced new _Resource.requirements class attribute where all Redmine plugins required by resource should be listed (preparations to support non-native resources)
• Added: New exceptions:
  • ResourceRequirementsError
• Fixed: It was impossible to set a custom field of date/datetime type using date/datetime Python objects
• Fixed: Issue #46 (A UnicodeEncodeError was raised in Python 2.x while trying to access a url property of a WikiPage resource if it contained non-ascii characters)