* Rebaseline firmware to non-OS SDK version 3.0
* Note that SDK version 3.0 introduces the concept of a Flash Partition Table(PT). This is located at Flash offset 0x10000 in our firmware build.
* The firmware is now PT aware with both LFS and SPIFFS taking their partition size and location from the PT
* A new tool `tools/nodemcu-partition.py` is now used to initialise these data and can also download LFS and SPIFFS images to these partitions.
Added `node.egc.meminfo()` to expose LVM usage (to make the regular
`node.egc.ON_MEM_LIMIT` option usable).
Extended the `node.egc.ON_MEM_LIMIT` option to also take negative limits,
in which case that's taken as a request to keep a certain amount of heap
available for non-Lua use.