amber.js tries to find itself also by id not just as last <script>

When loaded all scripts asynchronously, the
'last <script> tag' trick is unable to find the right one,
so amber.js does not see its path and possible data-libs.

In case of async loading, giving the <script> well-known id
'amber-path-mapper' allows it to find itself.
update CHANGELOG with async amber.js loading
Commenting 'amber-path-mapper' id in "find myself" part
Readable error for library dependencies missing
chunk of error reported
Fixes issue #774
Merge pull request #771 from herby/alternate-find-amberjs-script

amber.js tries to find itself also by id not just as last <script>
Merge pull request #772 from herby/gh-770

Helps some parts of #770
Alert error message when class compilation fails in Environment
Warn the user when subclassing nil
Adds support for generating methods in Helios

- Supports `initialize`
- Supports `getter`/`setter`
- Dispatches the generation stategy to the selected class
Fixes issue #775
fixes issue #777
Fix review
Fix double spaces
Merge pull request #778 from BenjaminVanRyseghem/master

Adds support for generating methods in Helios
Fixes #779
Adds more convenient testing methods on String

- adds `beginsWith:`
- adds `endsWith:`
Merge pull request #780 from BenjaminVanRyseghem/classifier

Adds more convenient testing methods on String
Moves `beginsWith:` and `endsWith:` to `SequenceableCollection`