Multiple small changes

[The-EDev]

This PR introduces multiple changes that I felt were too small to put into 4 different branches.

Changes are as follows:

1. Allow SSL certificate chain files (closes Added a function to enable SSL using a certificate chain #387)
2. have OPTIONS responses report content-length (fixes OPTIONS response without content-length #402)
3. Allow Doxygen to document SSL, compression, logging, and debug parts of Crow.
4. fixed several typos (overrides doxygen stop on errors, fix typo, fix doxygen comment #382)

Special Thanks to @jeanbiber for pointing out and fixing 1 and 2, and to @stephanecharette for pointing out some of the typos in 4.

Once this PR is merged, I'll copy some of the changes over to the v1.0 branch and prepare the release of v1.0+2

[crow-clang-format]

--- include/crow/app.h	(before formatting)
+++ include/crow/app.h	(after formatting)
@@ -376,10 +376,7 @@
             ssl_context_.use_certificate_chain_file(crt_filename);
             ssl_context_.use_private_key_file(key_filename, ssl_context_t::pem);
             ssl_context_.set_options(
-              boost::asio::ssl::context::default_workarounds
-              | boost::asio::ssl::context::no_sslv2
-              | boost::asio::ssl::context::no_sslv3
-              );
+              boost::asio::ssl::context::default_workarounds | boost::asio::ssl::context::no_sslv2 | boost::asio::ssl::context::no_sslv3);
             return *this;
         }