This fixes a 500 error / panic caused by ActivityPub actors without an
`inbox` or `outbox` attribute.

This doesn't change the actual underlying dependency; it simply uses the
current, most recent tag for the impart library.

This gets rid of the gorilla/context dependency, which might have been
causing a memory leak.

We noticed some serious memory leakage on Write.as that seemed to point
to this library. One heap snapshot:

      flat  flat%   sum%        cum   cum%
  259.13MB 30.41% 30.41%   268.13MB 31.46%  net/textproto.(*Reader).ReadMIMEHeader
  105.71MB 12.40% 42.81%   105.71MB 12.40%  github.com/gorilla/context.Set
   78.53MB  9.21% 52.03%   125.53MB 14.73%  github.com/gorilla/sessions.(*Registry).Get
   55.51MB  6.51% 58.54%    82.52MB  9.68%  net/http.(*Request).WithContext
   38.01MB  4.46% 63.00%    38.01MB  4.46%  github.com/gorilla/mux.extractVars
      35MB  4.11% 67.11%       53MB  6.22%  context.WithCancel
   34.50MB  4.05% 71.16%    34.50MB  4.05%  context.WithValue
      27MB  3.17% 74.32%       27MB  3.17%  net/http.cloneURL
      26MB  3.05% 77.38%       26MB  3.05%  github.com/gorilla/sessions.NewSession
      18MB  2.11% 79.49%       18MB  2.11%  context.(*cancelCtx).Done
   16.50MB  1.94% 81.42%    16.50MB  1.94%  syscall.anyToSockaddr
      14MB  1.64% 83.07%       47MB  5.52%  github.com/gorilla/sessions.(*CookieStore).New
   13.50MB  1.58% 84.65%    51.51MB  6.04%  github.com/gorilla/mux.(*Route).Match
   11.67MB  1.37% 86.02%    13.21MB  1.55%  regexp.(*Regexp).replaceAll
    9.72MB  1.14% 87.16%    22.94MB  2.69%  regexp.(*Regexp).ReplaceAllString
    9.50MB  1.11% 88.28%   115.21MB 13.52%  github.com/gorilla/sessions.GetRegistry

With the help of these articles, we tracked it down to this dependency,
and upgraded the library, which seems to have completely fixed the issue
so far:

https://rover.rocks/golang-memory-leak/
https://medium.com/@walterwu_22843/golang-memory-leak-while-handling-huge-amount-of-http-request-35cc970cb75e

This should fix #133

also run go mod tidy to clean up module files

This gives us our standard logging and passes around errors with
impart.HTTPError.

Ref T705

This fixes activityserve crashes caused by mentioning WriteFreely
instances.

be Note to work but I will open an issue for them and see what their
reaction will be.

this borrows some code from github.com/gogs/gogs/pkg/tool to avoid
pulling it in as a dependency, along with many other indirect deps.

now checking for and returning invalid content type errors

this updates to parse the time from the imported file, using v0.1.1 of
the wfimport library

this adds basic support for importing files as blog posts.

.txt and .md are supported at this time and the
collection is selectable, defaulting to draft.

if a collection is specified the post is federated.

This upgrades the library to v2, which lets you specify that GOMAXPROCs
should always be the max number of CPUs -- and then sets it to that.

One side effect of this is that images are no longer listed in sitemaps.
I'm somehow at a loss on how to build and append the images array we
need, with the library's latest changes.

Fixes #86

This adds https://github.com/jteeuwen/go-bindata as a module dependency
as the make target 'build' will result in it's addition.

This indicates whether or not invites are enabled on this instance. It
requires an upgrade to writefreely/go-nodeinfo v1.2.0