Remove part with no section.

asciidoctor from git complains about the user manual as follows:

  asciidoctor: ERROR: user-manual.adoc: line 1918: invalid part, must have at least one section (e.g., chapter, appendix, etc.)

Omit the part titled "Conclusion", as it is essentially empty and prevents
the document from being processed.  It can always be re-added later if
needed.
Update user manual to refer to DocBook 5.0.
Update DocBook example to use DocBook 5.
fix the explanation of file name of docinfo1 attribute in user manual.
Merge pull request #209 from bk2204/user-manual-build

Remove part with no section.
Merge pull request #210 from bk2204/user-manual-docbook5

Update user manual to refer to DocBook 5
Merge pull request #212 from pasberth/master

fix the explanation of file name of docinfo1 attribute in user manual.
Only lines from AsciiDoc files are preprocessed.
resolves #215 fix footnoteref example
add testimonial to homepage
set the default Ruby version to 2.1
fix layout of testimonal
add note about DNS records in README [ci skip]
link to GitHub help page on DNS records [ci skip]
Merge pull request #213 from bk2204/non-asciidoc-preprocess

Only lines from AsciiDoc files are preprocessed.
documentation for asciidoctor/asciidoctor#737

- make note that substitution are not applied to passthrough blocks by
  default starting with Asciidoctor 1.5.0
Update install-and-use-asciidoctor-java-integration.adoc

Corrected two examples that show the use of Collections.<String,Object>emptyMap() to create an empty map as the options parameter. Doing this results in a Java UnsupportedOperationException at runtime because AsciiDoctor is trying to put something in the immutable map that's returned (see stack trace below).

java.lang.UnsupportedOperationException
	at java.util.AbstractMap.put(AbstractMap.java:203)
	at org.asciidoctor.internal.JRubyAsciidoctor.addRubyRuntimeAsAttribute(JRubyAsciidoctor.java:174)
	at org.asciidoctor.internal.JRubyAsciidoctor.renderFile(JRubyAsciidoctor.java:158)
Merge pull request #217 from clintfoster/patch-1

Update install-and-use-asciidoctor-java-integration.adoc
add @iandarwin to list of O'Reilly authors using AsciiDoc
fix punctuation