Improved declaration and handling of AnalysisMethodAttribute
Added a slightly better logo.
Tweaks to logos/icon.
Merge pull request #48 from sharwell/attribute-usage

Improved declaration and handling of AnalysisMethodAttribute
Merge pull request #49 from DanTup/master

Slightly more unique logo/icons.
Update Analysis Service snapshot.

Fixes missing line numbers for SDK entities.
Merge pull request #50 from DanTup/master

Update Analysis Service snapshot.
Use an analysis service factory to support asynchronous creation of the service (fixes #45)
Download the Dart SDK on demand if not found locally (fixes #46)
Refactor code to place several constants in shared locations