doc: Trivial spelling and consistency update

docs/design/design-rtpretransmission.txt

@@ -18,7 +18,7 @@ element when it receives a NACK from the network.
 rtprtxsend element
 ------------------
 
--- basic mecansim
+-- basic mechanism
 
 rtprtxsend keeps a history of rtp packets that it has already sent.
 When it receives the event GstRTPRetransmissionRequest from the downstream
@@ -49,7 +49,7 @@ To choose rtx_ssrc it randomly selects a number between 0 and 2^32-1 until
 it is different than master_ssrc.
 rtx_seqnum is randomly selected between 0 and 2^16-1
 
-- deeper in the stored buffer history
+-- deeper in the stored buffer history
 
 For the history it uses a GSequence with 2^15-1 as its maximum size.
 Which is resonable as the default value is 100.
@@ -86,7 +86,7 @@ So that it can be handled by the rtppayloader.
 rtprtxreceive element
 ------------------
 
--- basic mecanims
+-- basic mechanism
 
 The same rtprtxreceive instance can receive several master streams and several
 retransmission streams.
@@ -141,7 +141,7 @@ A stored request actually means that actually the couple seqnum,ssrc is stored.
 If it's happens the request is droped but it avoids to do bad associations.
 In this case the association is just delayed to the next request.
 
-- building original packet from rtx packet
+-- building original packet from rtx packet
 
 Header, extensions, payload and padding are mostly the same. Except that the
 OSN is removed from the payload. Then ssrc, seqnum, and original payload type