Report better error messages for vcpkg projects and features

[ZehMatt]

This will now give better error messages, some might not know that vcpkg has reserved names so this will better communicate that.

The errors will show following:

>cmkr gen
[cmkr] error: Invalid vcpkg package name 'core', name is reserved

>cmkr gen
[cmkr] error: Invalid vcpkg package feature 'core', name is reserved

[mrexodia]

Sehr gut