Simplify the editing of tooth.json

[RedbeanW]

Is your feature request related to a problem? Please describe.

The writing of tooth.json is sometimes troublesome.

Describe the solution you'd like

• Remove placement, provide a directory like content that maps to the root of the BDS.
• Lowercase URLs should not be enforced, this work should be done by LIP.

[Andy Zijian Zhang]

placement field must be preserved for conditional installation, e.g. per-GOOS installation.

Uppercase letters in URLs are already supported. The stale documentation has been updated.