reconciling origin and RP ID handling (#464)

* polish RP ID dfn

* polish authn & regstn dfns

* alphabetize terminology

* minor edits

* decorate all RP ID occurances

* figuring out rpId issues, modest edits to improve issue #414

* fixup RP ID ddfn and rpId handling, improves #255, #259, #260, #416

* fix RP ID dfn, fix descriptions of RP ID's value, improves #255, #259, #260, #416

* more RP ID polishing

* fixup my errors (thx jcjones), cleanup, fix #323

* swap order of CredentialCreationOptions and CredentialRequestOptions sections

* fix confusion of CredentialRequestOptions wrt CredentialCreationOptions

* begin align markup approach of the makeCred and getAssn sections

* |publicKeyOptions| -> |options|

* move {#sctn-user-credential-params} to proper section, minor editing

* decorate title of {#authenticatorSelection} section

* add internal cross-refs

* add internal cross-refs

* clarify title of {#getAssertion}

* complete applying RP ID fixup to {#getAssertion}. thanks bzbarsky & jyasskin, fixes #255, #259, #416

* document RP ID restrictions and relaxations, fixes #260, thx bzbarsky!

* add 'valid domain' restriction placeholder

* addressing jyasskin's feedback -- thanks!

* fix #467

* delete a blank...

* fix various items per jyasskin - thxcls

* |foo|['{{bar}}'] style to <code>|options|.{{bar}}</code> style - thx jyasskin :)