Now we can do REST API request by creating CurlJsonRequest and waiting
for it to call our callback. Passed pointer is Common::JSONValue.
This commit also does some minor variable renaming fixes.
Now it is based on MemoryReadWriteStream, which is introduced by this
commit. This stream is using ring buffer and is dynamically increasing
its size when necessary.
NetworkReadStream actually saves whole response in the memory now.
There is a pause mechanism in libcurl, but if libcurl is requesting
something compressed, it would have to uncompress data as it goes even
if we paused the request. Even though our own stream won't be notified
about this data when when "pause" the request, libcurl's own buffer
wound be expanding.
CurlRequest uses own multi_handle, in which it creates an easy_handle to
make a request.
Every time `handle()` is called it checks whether request is complete
and, if it is, stops.
