Removed octet-vector in src/types.lisp

* src/types.lisp (octet-vector): removed; `nibbles:octet-vector' is
  used instead
* src/ffi.lisp (%process-regular-message): adapted ftype declamation
  (%process-membership-message): likewise
  (%send-one): likewise
  (%send-multiple): likewise
  (%extract-groups): likewise
* src/connection.lisp (send connection string simple-array): change
  type check octet-vector -> simple-octet-vector
  (send connection sequence simple-array): likewise
* src/package.lisp (package network.spread): added used package
  nibbles; removed exported symbol octet-vector
* test/package.lisp (package network.spread.test): added used package
  nibbles
* network.spread.asd (system network.spread): added system dependency
  on nibbles
Removed AUTHORS file

* AUTHORS: removed; the ASDF system covers this
Added receive-into in src/connection.lisp

* src/protocol.lisp (header): updated copyright
  (receive-into): new generic function; receive data into an existing
  buffer
  (receive): added return-sender? and return-groups? keyword
  parameters; extended documentation string
* src/connection.lisp (receive-into connection simple-array): new
  method; receive into a given buffer
  (receive connection): allocate a buffer and use `receive-into';
  added keyword parameters return-sender? and return-groups? to
  control whether sender and/or groups should be extracted and
  returned
* src/ffi.lisp (spread-receive): declared inline; prevent to/from
  string conversion of sender
  (with-pointers-to-vector-data): new macro; convenience wrapper for
  `cffi:with-pointer-to-vector-data'
  (%extract-type): renamed %type->tag -> %extract-type
  (%extract-sender): new function; extract sender string from buffer
  (%extract-groups): handle "buffer too small case"; use
  `sb-ext:octets-to-string' on SBCL
  (%receive-into): renamed %receive -> %receive-into; receive into
  existing buffer; return type, sender and groups as multiple values;
  only return requested objects
  (%process-regular-message): removed; no longer used
  (%process-membership-message): likewise
* src/package.lisp (package network.spread): added exported symbol
  receive-into
* test/connection.lisp (connection-root::send-receive/smoke): renamed
  send-receive -> send-receive/smoke; test :return-groups?,
  :return-sender? keyword parameters
  (connection-root::send-receive-into/smoke): like send-receive/smoke
  but for `receive-into'
Added support for un/reloading the Spread library in src/reloading.lisp

* src/reloading.lisp: new file; contains support for unloading and
  reloading the Spread library
* src/package.lisp (package network.spread): added exported symbols
  unload-spread-library, reload-spread-library and
  enable-reload-spread-library
* network.spread.asd (system network.spread): added file
  src/reloading.lisp