0.4.0

Release content for version 0.4.0

• feat: add timestamp when emitting stdout and stderr events (process.js)
• feat: add extra function to fallback to a default value when a command line argument is missing (arg.js)
• feat: allow to pass custom properties to Process constructor (process.js)
• feat: possibility to use custom buffer size when reading from child process streams (process.js)
• refactor: set default buffer size to 512 bytes
• fix: remove loop when reading from child process