Fix broken javadoc links in reference guide

Replace links in the reference documentation from
`http://static.springsource.org/spring/docs/current/api/..` to
`http://docs.spring.io/spring/docs/current/javadoc-api/..`

Issue: SPR-11087
Replace non UTF-8 characters in asciidoc source

Replace the odd instance of non UTF-8 characters in the reference
asciidoc source, mainly smart-quotes.

Issue: SPR-11096
Add .gradletasknamecache to .gitignore
Replace springsource.org links with spring.io

Update reference documentation links to use the new spring.io domain.

Issue: SPR-11096
Wrap reference asciidoc at 90 characters

Reformat the asciidoc source for the reference guide to wrap at about
90 characters.

Issue: SPR-11096
Replace asciidoc authors convention with attribute

Replace the second line of the asciidoc reference guide that, by
convention, specifies authors with an 'author' explicit attribute.

Issue: SPR-11096
Specify asciidoc type

Specify a specific asciidoc type of 'docbook' to prevent
'multiple titles at level 0' errors during generation.

Issue: SPR-11096
Remove superfluous space before 'http' in asciidoc

Remove the superfluous space that appears before each 'http' reference
in the asciidoc source. Presumably there due to some quirk of the
docbook conversion.

Issue: SPR-11096
Fix broken reference guide links

Remove or replace broken links from the reference documentation.

Issue: SPR-11096
Upgrade to Gradle 1.8 and propdeps 0.0.5
Polish build.gradle
Remove superfluous spaces in asciidoc

Remove the superfluous spaces that appear in the asciidoc source.

Issue: SPR-11096
Add whitespace to improve asciidoc readability

Issue: SPR-11096
Restore multi-page and PDF reference documentation

Generate docbook xml from the asciidoc reference guide and use the
docbook-reference-plugin to generate HTML (single and multi-page) and
PDF documentation.

Issue: SPR-11096
Fix standard multipart binding + Polish

Fixing standard multipart binding when multiple parts share
the same name.

Uncomment previously @Ignored tests now that Jetty supports
Servlet 3.0 spec.

Issue: SPR-10591
Upgrade Jetty to 9.1.0 GA

Issue: SPR-11099
Rely on presence of Servlet 2.5's ServletContext.getContextPath()
Polishing
Defensively handle non-retrievable ApplicationListener bean names
Allow instrumentation to be used with Attach API

Update InstrumentationSavingAgent to allow it to be used with the
Attach API

Issue: SPR-11083