If the If-None-Match header is supplied with a previously
obtained ETag from the same query, a 304 Not Modified is
returned with no content.

This allows clients to completely leverage the ETag header.
Signed-off-by: Kevin Morris <kevr@0cost.org>

Since we're in the hot path, a constant re.compiled
JSONP_EXPR is defined for checks against the callback.

Additionally, reorganized `content_type` and `content`
to avoid performing a DB query when we encounter a
regex mismatch.
Signed-off-by: Kevin Morris <kevr@0cost.org>

This change introduces alternate rendering of text/javascript
JSONP-compatible callback content. The `examples/jsonp.html`
HTML document can be used to test this functionality against
a running aurweb server.
Signed-off-by: Kevin Morris <kevr@0cost.org>

Signed-off-by: Kevin Morris <kevr@0cost.org>

This commit introduces a PackageSearch-derivative class: `RPCSearch`.
This derivative modifies callback behavior of PackageSearch to
suit RPC searches, including [make|check|opt]depends `by` types.
Signed-off-by: Kevin Morris <kevr@0cost.org>

Signed-off-by: Kevin Morris <kevr@0cost.org>

The ETag header can be used for client-side caching.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag

Signed-off-by: Kevin Morris <kevr@0cost.org>

New configuration options:

- `[ratelimit] cache`
    - A boolean indicating whether we should use configured cache (1)
      or database (0) for ratelimiting.
Signed-off-by: Kevin Morris <kevr@0cost.org>

This reworks the base implementation of the RPC to use a
class called RPC for handling of requests. Took a bit of
a different approach than PHP in terms of exposed methods,
but it does end up achieving the same goal, with one additional
error: "Request type '{type}' is not yet implemented."

For FastAPI development, we'll stick with:

- If the supplied 'type' argument has an alias mapping in
  RPC.ALIASES, we convert the type argument over to its alias
  before doing anything. Example: 'info' is aliased to 'multiinfo',
  so when a user requests type=info, it is converted to type=multiinfo.
- If the type does not exist in RPC.EXPOSED_TYPES, the following
  error is produced: "No request type/data specified."
- If the type **does** exist in RPC.EXPOSED_TYPES, but does not
  have an implemented `RPC._handle_{type}_type` function, the
  following error is produced: "Request type '{type}' is not yet
  implemented."
Signed-off-by: Kevin Morris <kevr@0cost.org>

This feature of RPC is required to take advantage of
javascript typeahead.
Signed-off-by: Kevin Morris <kevr@0cost.org>

Signed-off-by: Kevin Morris <kevr@0cost.org>

PHP does this, we should persist the behavior here for
v=5.
Signed-off-by: Kevin Morris <kevr@0cost.org>