Fix miscellaneous Sphinx warnings (#244)

* /index.rst:24: WARNING: Line block ends without a blank line.

* /install.rst:300: WARNING: Explicit markup ends without a blank line; unexpected unindent.

* /admin.rst:273: WARNING: Could not lex literal_block as "http". Highlighting skipped.

* /tutorials/tut1.rst:150: WARNING: Could not lex literal_block as "json". Highlighting skipped.

* Remove extra newline

* Use integer value as epoch in JSON snippet

Even though using a string value is convenient (due to the lack of JSON
comments), it is confusing since the value should actually be an
integer. A slightly more verbose documentation is therefore preferable.

install.rst

@@ -297,10 +297,11 @@ The database connection string above is just an example. Adjust the role and pas
   .. code-block:: bash
 
     listen_addresses = 'localhost,10.0.0.10'
+
   You might also need to add a new IPv4 local connection within pg_hba.conf. For instance:
-  
+
   .. code-block:: bash
-  
+
     host    all             all             10.0.0.10/32            trust
 
 Containerized PostgREST *and* db with docker-compose