Interfaces should start with an I by convention

[weitzhandler]

Hi,

As per .NET's naming conventions, interface names should alway start with an additional I.
Please check this for more info.

The Gedcom X library interfaces do not obey to this convention.
Here are some:

• GedcomxEntryDeserializer
• GedcomxEntrySerializer
• SupportsLinks
• GedcomModelVisitor
• Attributable

Although this is obviously a breaking change, I believe this has no effect, I think we can assume nobody have directly implemented these interfaces.

[BrannonKing]

+1. Do it right.

[stoicflame]

See #26.