feat(modules): builtin shodan scan as module

[0x4bs3nt]

First part of completing the #52 issue by making requested complex Go scans available as modules.

Summary

• Allows complex Go scan; shodan, to participate in the sif module system

Features

• Made Go scan for shodan available as a module
• Added to module registry
• Will show up in the -lm/-list-modules

Test plan

• gofmt applied
• all unit tests passing
• go vet passes
• manually tested shodan works the same as a module and as a legacy Go scan