Local webserver's helper class, Reader, supported simple GET requests and POST form/multipart ones. The code for the latter was a bit specific, and didn't allow handling more generic POST requests.
This change adds ReaderMode enum, with RM_HTTP_GENERIC mode, that allows such generic requests to be handled. In Networking::Client class, that uses Reader, readContent() was renamed to readFirstContent(), and corresponds to previously existing POST form/multipart mode. readContent() should now be used for generic POST requests handling.
Now Client reads the first headers block, then LocalWebserver decides
which Handler to use. In case of "/upload", UploadFileHandler is used.
But now it only knows the "path" parameter. If that's valid, actual
UploadFileClientHandler is created, which reads the contents of the
request and, when finds there an "upload_file" field, starts saving it
in the directory specified by "path".
With that we don't need temp files approach from Reader class.
That ClientHandler is made for responding GET requests. It calculates
stream's length, it allows to specify response code and headers, it can
be used to transfer any ReadStream.
