MemberSearch cleanup and polish

[mtodd]

As a follow up to #64, this renames GitHub::Ldap::Members member search strategy to GitHub::Ldap::MemberSearch and aims to finish up any significant missing pieces:

• configuration
• Active Directory strategy (followup?)
• detect strategy

cc @jch

[jch]

This module feels like a premature extraction. It's specific to ActiveDirectory, and doesn't seem useful outside this context.

[mtodd]

@jch agree in some senses, but there are two separate classes that depend on the same behavior that didn't feel right duplicating in (the ActiveDirectory MemberSearch and MembershipValidation strategies). It's a mix of AD-specific feature detection with general capability exposure.

I'm not crazy about it, but it unblocks this PR and can be easily changed in the future when a better approach can be considered, particularly because it's internal only. I think this need will diminish with the changes you outline in #69 (comment), so it is likely temporary.

Thoughts?

[mtodd]

@jch so to summarize what needs to be addressed in a followup PR:

• reduce detect_strategy's knowledge of strategy internals
• give configuration more responsibility (setting the strategy object, defaulting)
• move Active Directory capability sniffing functionality (either more central, or more context-specific)
• possibly remove detect as a meta-strategy and incorporate into default configuration handling

Does that sound like a reasonable breakdown? Some of it may be more specific that necessary, partly because I think there are a few directions we could go that would result in cleaner internals with equivalent functionality, but exactly what I've not concluded.

[jch]

👍 to shipping if you feel it'll unblock your other work. Left comments inline about refactorings.