refactor(grunt-espower): switch dependency espower-source to espower

https://gist.github.com/twada/103d34a3237cecd463a6
feat(grunt-espower): initial support for multi stage sourcemap
refactor(grunt-espower): improve sourceRoot resolution
test(grunt-espower): add coffeescript demo with SourceMap
test(grunt-espower): add typescript demo with SourceMap
test(grunt-espower): add compatibility test for espower generated code
chore(grunt-espower): update .gitignore
test(grunt-espower): add multi ts sample
chore(grunt-espower): update dependency. multi-stage-sourcemap 0.1.1 to 0.2.1
test(grunt-espower): add compatibility test for espower generated code. multi-ts
refactor(grunt-espower): finish TODO in tasks/espower.js
refactor(grunt-espower): extract function. it named `resolveOutgoingSourcesInfo`
test(grunt-espower): add compatibility test for espower generated code. embed base64 format
fix(grunt-espower): fix invalid sourcemap generation in single-stage process
Merge pull request #2 from twada/wip-support-multistage-sourcemap

support multistage sourcemap