v2.11: C Implementation of Archive Get

Bug Fixes:

* Fix possible truncated WAL segments when an error occurs mid-write. (Reported by blogh.)
* Fix info command missing WAL min/max when stanza specified. (Fixed by Stefan Fercot.)
* Fix non-compliant JSON for options passed from C to Perl. (Reported by Leo Khomenko.)

Improvements:

* The archive-get command is implemented entirely in C.
* Enable socket keep-alive on older Perl versions. (Contributed by Marc Cousin.)
* Error when parameters are passed to a command that does not accept parameters. (Suggested by Jason O'Donnell.)
* Add hints when unable to find a WAL segment in the archive. (Suggested by Hans-Jürgen Schönig.)
* Improve error when hostname cannot be found in a certificate. (Suggested by James Badger.)
* Add additional options to backup.manifest for debugging purposes. (Contributed by blogh.)

doc/RELEASE.md

@@ -30,7 +30,8 @@ if (!$bTest)
 
 - Copy coverage report:
 ```
-cd doc/site
+cd <pgbackrest-base>/doc/site
+rm -rf coverage
 cp -r ../../test/coverage/c coverage
 ```
 
@@ -63,7 +64,7 @@ with:
 
 - In `doc/site/coverage` replace:
 ```
-            <td class="headerValue">all C unit</td>
+            <td class="headerValue">all.lcov</td>
 ```
 with:
 ```
@@ -72,6 +73,6 @@ with:
 
 - Switch to prior dir and copy coverage:
 ```
-doc/site/prior/X.XX
+cd ../prior/X.XX
 cp -r ../../coverage .
 ```