docs: rewrite to present tense

... instead of using future tense.

+ numerous cleanups and improvements
+ stick to "reuse" not "re-use"
+ fewer contractions

Closes #11713

docs/HTTP2.md

@@ -55,14 +55,14 @@ connection.
 
 To take advantage of multiplexing, you need to use the multi interface and set
 `CURLMOPT_PIPELINING` to `CURLPIPE_MULTIPLEX`. With that bit set, libcurl will
-attempt to re-use existing HTTP/2 connections and just add a new stream over
+attempt to reuse existing HTTP/2 connections and just add a new stream over
 that when doing subsequent parallel requests.
 
 While libcurl sets up a connection to an HTTP server there is a period during
 which it does not know if it can pipeline or do multiplexing and if you add
 new transfers in that period, libcurl will default to start new connections
 for those transfers. With the new option `CURLOPT_PIPEWAIT` (added in 7.43.0),
-you can ask that a transfer should rather wait and see in case there's a
+you can ask that a transfer should rather wait and see in case there is a
 connection for the same host in progress that might end up being possible to
 multiplex on. It favors keeping the number of connections low to the cost of
 slightly longer time to first byte transferred.