Release v0.6.0

Features:

• Implement modal component as feature
• Include Apache 2.0 license with MIT (as yew and rust)

Fixes:

• Fix example in button documentation. [@Bandsberg]
• Fix typo in Readme. [@zoechi]

Improvements:

• Change deprecated handle events

Breaks:

• Change the handle event onkeypress_signal to onkeydown_signal in each component
  that is used