Fix checks of startIndex and itemsPerPage in ListResponse

[sleelin]

Currently on instantiation, the ListResponse class will check that the startIndex and itemsPerPage properties are integer values greater than or equal to 1 and 0 respectively, and throw a TypeError if not. This was intended to prevent the use of invalid values in bespoke implementations. According to RFC7644, startIndex and itemsPerPage values less than this should be treated as being 1 and 0 respectively. This rounding is already implemented in the ListResponse constructor, but is functionally unused, as the constructor will throw the TypeError first.

This change removes the minimum integer value check from the ListResponse constructor (fixes #42), and rounds startIndex and count integer constraints to their minimum values in the SCIMMY.Types.Resource constructor. Test fixtures have also been updated to reflect this change, and will now check for more non-number values in place of non-positive integers.