Refactor to dry up code

[lavafroth]

Changes

• Use switch statement on interface{}s instead of reflection to figure out types (bumped go version to 1.20)
• Avoid goto statements when possible
• Use mapset library for blocklists and looking up previously seen URLs
• Lazily construct structures when errors are involved
• Set a log level when parsing configs to avoid checking the verbose flag for every logrus log invocation
• Scope loop variables to respective blocks
• Minor improvements to conditional statements that employ string formatting

[lc]

Thanks for the PR! Looks great