Use httpmock 0.8

[jayvdb]

Closes #904

Only partially done; more changes needed described on the issue above. Then I ran into httpmock/httpmock#183 so my own testing is not complete.

[danieleades]

would be great if this could get merged after httpmock/httpmock#206 is merged, since this addresses some bugs in progenitor's mock codegen

[ahl]

would be great if this could get merged after httpmock/httpmock#206 is merged, since this addresses some bugs in progenitor's mock codegen

Did #1264 obviate the need for this or is it still relevant?

[danieleades]

would be great if this could get merged after httpmock/httpmock#206 is merged, since this addresses some bugs in progenitor's mock codegen

Did #1264 obviate the need for this or is it still relevant?

Stil need that upstream change into httpmock, and then the updated httpmock used in progenitor. The reason being that progenitor can generate mocks that attempt to pass &str to Then::json_body_obj, which fails to compile because of needlessly restrictive trait bounds on that method

[ahl]

I meant: do we still need this PR.