Improve code quality and legibility

[kamushadenes]

This PR intends to improve Golang code quality and legibility to facilitate future changes.

A non-exhaustive list of changes is:

• Remove a ton of dead code / unused functions and vars in order to simplify review and auditing
• Simplify some nested ifs that made the code hard to read (there are many left though)
• Where applicable, replace if-else with switch-case
• Replace many instances of strings.Index() checks with strings.Contains()
• Replace strings.HasSuffix() + Trim with non-conditional strings.TrimSuffix()
• Use var <name> <type> instead of <name> := <type>(zero value)
• Replace var names that conflicted with reserved keywords (len, close, etc...)
• Properly handle ineffectual assignments (like errs that weren't checked etc)
• Remove unnecessary fmt.Sprintf() on non-formatting strings
• Remove a bunch of redundant returns
• Remove a bunch of unnecessary / redundant conversions
• Simplify expressions such as x = x + y => x += y
• Replace string(r.Bytes()) with r.String() in *bytes.Buffer instances.
• Format files using go fmt
• Replace some strings with consts, such as POST => http.MethodPost and 200 => http.StatusOK (there are still many repeated strings that could become consts)
• Use append(slice, newSlice...) instead of a for loop
• Use raw strings in regex.MustCompile
• Fix instances of == true and if cond == true ... return true ... else return false
• And others

There are still many improvements to be made, but this PR was already too big so I'll make separate PRs after this one (hopefully) gets merged.

@esimkowitz I need help testing this. It shouldn't change anything (besides perhaps throwing some errors that were previously incorrectly ignored), but better safe than sorry.

[esimkowitz]

Closing as we've made significant changes to Wave with v0.8 that make these changes no longer relevant