This handles the case where the supplied value for minItems is an integer

This is necessary because you can get into an odd situation where you supply a schema
as a map[string]interface{} with minItems being a native int in Go and gojsonschema
complains that the value isn't an integer.
Added utility routines for common patterns
Updated a few cases to use new utility functions
Some cases using mustBeInteger utility function
More conversions and fixed a few variable name typos
Last cases converted to utility routines mustBeInteger and mustBeNumber

Overall, I think the code is much cleaner as a result of these changes.  There is a lot less
boilerplate code and no loss of generality or clarity (IMHO).
Merge pull request #38 from xogeny/master

Inconsistent handling of integers vs. numbers