Zkg should fail quicker if features conflict

[pauldokas]

Zkg should fail quicker if features conflict. For example, the following use case should fail before asking me a bunch of questions instead of making me enter a bunch of information and then failing.

% zkg create --packagedir foobar --features license plugin spicy-file-analyzer spicy-packet-analyzer spicy-protocol-analyzer
"package-template" requires a "name" value (the name of the package, e.g. "FooBar" or "spicy-http"):
name: FooBar
"package-template" requires a "namespace" value (a namespace for the package, e.g. "MyOrg"):
namespace: MyOrg
"package-template" requires a "analyzer" value (name of the Spicy analyzer, which typically corresponds to the protocol/format being parsed (e.g. "HTTP", "PNG")):
analyzer: HTTP
"package-template" requires a "protocol" value (transport protocol for the analyzer to use: TCP or UDP):
protocol: TCP
"package-template" requires a "unit" value (name of the top-level Spicy parsing unit for the file/packet format (e.g. "File" or "Packet")):
unit: File
"package-template" requires a "unit_orig" value (name of the top-level Spicy parsing unit for the originator side of the connection (e.g. "Request")):
unit_orig: Request
"package-template" requires a "unit_resp" value (name of the top-level Spicy parsing unit for the responder side of the connection (e.g. "Reply"); may be the same as originator side):
unit_resp: Reply
"package-template" requires a "author" value (your name and email address):
author: user@example.com
"package-template" requires a "license" value (one of apache, bsd-2, bsd-3, mit, mpl-2):
license: bsd-3
error: template input invalid, the "plugin" and "spicy-protocol-analyzer" features are mutually exclusive

[pauldokas]

And while I'm here. Dropping spicy-protocol-analyzer from the list of selected features doesn't seem to have any effect. Zkg is still complaining of a mutual exclusion conflict for spicy-protocol-analyzer even though it was not selected. Perhaps it was pulled in through a dependency?

% zkg create --packagedir foobar --features license plugin spicy-file-analyzer spicy-packet-analyzer
"package-template" requires a "name" value (the name of the package, e.g. "FooBar" or "spicy-http"):
name: FooBar
"package-template" requires a "namespace" value (a namespace for the package, e.g. "MyOrg"):
namespace: MyOrg
"package-template" requires a "analyzer" value (name of the Spicy analyzer, which typically corresponds to the protocol/format being parsed (e.g. "HTTP", "PNG")):
analyzer: HTTP
"package-template" requires a "unit" value (name of the top-level Spicy parsing unit for the file/packet format (e.g. "File" or "Packet")):
unit: File
"package-template" requires a "author" value (your name and email address):
author: user@example.com
"package-template" requires a "license" value (one of apache, bsd-2, bsd-3, mit, mpl-2):
license: bsd-3
error: template input invalid, the "plugin" and "spicy-protocol-analyzer" features are mutually exclusive

[bbannier]

I opened #22 to fix the incorrect error message.

As for triggering validation errors earlier, this is not a quick and easy fix as template validation only runs after all parameters have been collected.