'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
Links to version-scheme.adoc added
Page completed
Links on invokedynamic-support.html added. Section "Legacy Groovy 1.0" updated
Page modified for a single version.
Page completed
Page completed
Pictures were moved to doc/assets/img
Links to the pictures were changed.
Merge branch 'doc-windows-installer' of https://github.com/bura/groovy-core into doc-windows-installer

Conflicts:
	src/spec/doc/windows-nsis-installer.adoc
Merge pull request #223 from bura/doc-invoke-dynamic-support

New page "InvokeDynamic support" added
minimal formatting change