Stable: New APIs to list available platforms
Changes:
- New Python API:
mbedls.list_platforms()lists available platforms' names (unique list).mbedls.list_platforms_ext()lists platforms and their count in the system.
 - CLI options updated to reflect Python API changes:
- Option -p shows available platforms in JSON indented format.
 - Option -P shows platform count information in indented JSON format.
 
 - v0.1.16 documentation update (APIs examples).