Kernel: add Smalltalk>>#globalJsVariables
SemanticAnalyzer: use #globalJsVariabls in #errorUnknownVariable: method
Smalltalk: methods for adding/removing global JS variables
amberc.js: add js globals support
grunt-amberc.js: add support for JS globals
amberc: add support for JS globals
amber-cli: recompile
Update API-CHANGES.txt

add Smalltalk>>addGlobalJsVariable: and Smalltalk>>deleteGlobalJsVariable:
Kernel-Objects: remove '^self' from #add/#deleteGlobalJsVariable methods
Merge pull request #523 from mkroehnert/compiler

Add support for managing JS global variables needed by the compiler
Enhanced Amber REPL.
save previous results; Ctrl+L to clear screen
DRYed; also: assign new variables only if necessary
refactored too long repl methods
do not count up res names for no reason
refactoring: method names, multi value returns
fixed exception on empty line; generalised commands
Merge pull request #524 from machisuji/repl

Amber REPL Enhancements