Adds symlink to File

implementation of feature request #2114
Compiler now mentions which file has a duplicated module. Fixes #2131
Fix two test cases
Fix compile error during boostraping
Removed superfluous 'be'
Merge pull request #2241 from stoft/master

Grammar, removed superfluous 'be'
Merge pull request #2240 from gmcabrita/fix-duplicated-module

Improve compiler message when duplicated modules are detected
Hide module's location attribute
Create remote funs even in &mod.fun/arity, closes #2133
Merge pull request #2123 from duksis/symlink_on_file

Adds symlink to File
Rename symlink to ln_s according to File's convention
Use rebar hosted on S3
Ensure aliases are respected on root, closes #2227
Improve docs for generated apps
Use Exception.message/1 instead of exception.message
Update CHANGELOG
Soft deprecate is_exception/1 in favor of Exception.exception?/1
Implement default pop/2, pop/3, update/4, update!/3 for Dict.Behaviour
Convert ExUnit.Test and ExUnit.TestCase to structs
Improve application error formatting

* Format (nested) supervision tree init failures
* Format :gen_server exit reasons
* Fixes :invalid_options text
* Fixes text when when application start returns {:error, reason}