Extract some specs which are related to project rather than CLI
Run CLI specs in isolated environment

Previously, the specs were run in the project directory.
This fixes #119.
Fix odd indentations
Remove unnecessary test directory creation
Change FileHelper#create_file to add line feed to end of file
Refactor CLI specs with FileHelper#create_file
read_source cleanup
Merge pull request #134 from jurriaan/better-read_source

read_source cleanup
Merge pull request #135 from yujinakayama/refactor-cli-spec

Refactor CLI spec