This reverts commit 8463946e2d6b211208c04eb6832f155865d12de3, reversing
changes made to 8cf5d50560.

this changes the JSON tags to include both the ID and Collection
in PostParams. Both will be omitted when empty to maintain any unknown
backwards compatibility.

for creating or updating posts.

Fixes bug introduced when we moved `Token` into the func's parameters,
out of PostParams.

Moves the ID and token params out of PostParams and into the func's
parameters. A currently-unused `collection` parameter is left in for the
future, when the backend supports updating and deleting collection posts
via slug, not post ID.

Previously, they all said the same thing

writeas.github.io/docs -> developer.write.as/docs/api

Plus break up internal request building so we can optionally send query
parameters with some requests (like DELETEs!)

Plus change Post's ModifyToken to Token.

Plus fix Client post func and rename SubmittedPost to PostParams.

Includes ability to make authenticated requests and get posts.