Version 0.2.6

[AtiyahElsheikh]

resolves #23 #40 progresses #31 #34 #28 & #29

• improved data structure for Town
• constant for undefined house (related routines can return one type)
• Improved implementation of allocation algorithms (no temporary arrays)
• tuning do marriage algorithm (memoization can be avoided)
• Improved runtime performance (3x faster & 4x less memory allocation and storage)