Don't use markdown syntax in javadoc or error messages

[wilkinsona]

Classes and utilities designed to work with the `javax.servlet` specification.

It should probably be {@code javax.servlet} instead.

[philwebb]

We actually have quite a few more than just that package. I'll increase the scope of this and do a sweep to remove them all.

[wilkinsona]

Reopening to reinstate the use of backticks where the text is ultimately rendered using Asciidoctor and to use ' in configuration property javadoc comments.