0.2.0 Documentation update

[SpicyPete]

Update documentation on developer.bitcoin.com for 0.2.0

Topics to update

• Repeatable payments
• Absolute BCH amounts
• SLP if it makes it in this release
• QR Codes and URI
  • Watch all for payments
  • controlled step from app.

[SpicyPete]

Completed in developer.bitcoin.com repo