GROOVY-6268: First bits of tools documentation
   * reorganized layout for tools section
   * introduced files for each subsection
   * documentation for groovyc CLI
   * documentation for groovyc Ant task
   * documentation for joint compilation
GROOVY-6268: section on keywords and possibility to use keywords as identifiers after dots
GROOVY-6268: shebang line comment
GROOVY-6268: use font-awesome's icons
GROOVY-6268: multiline comment section
GROOVY-6268: correct escaping for the multiline comment delimiter
GROOVY-6268: Maven docs
   * fixed cross reference links
   * added sections on GMaven, GMavenPlus, GMaven2 and Groovy Eclipse
   * fixed leveloffset
GROOVY-6268: Introduction
   * temporarily set the TOC level to 10 (gives a better idea of the contents while editing)
   * fix bullets of introduction
GROOVY-6268: Use prettify (best highlight so far)
GROOVY-6268: Add license and contributors sections
GROOVY-6268: groovydoc comment section
'Install Groovy' section added
Introduction added
Page structure added
Restructure page. The proposal to change.
Title "IDE plugin" changed. Typo fix.
"Groovy 2.1" section filled.
"Groovy 2.2" section filled.
Page "core-getting-started.adoc" finished (Some links are require clarification).
".groovy" removed in shell expression