Core refactoring: break out VFS and OTA into libs

OTA nad VFS code is moved into libraries. Less

The following new libraries are added:

  - https://github.com/mongoose-os-libs/core
  - https://github.com/mongoose-os-libs/ota-common
  - https://github.com/mongoose-os-libs/vfs-common
  - https://github.com/mongoose-os-libs/vfs-fs-spiffs
  - https://github.com/mongoose-os-libs/vfs-dev-ram

"core" is the point where filesystem and config are initialized.
Most "normal" libraries and apps should depend on it and for the nothing much changes.
VFS and OTA libraries need to pay more attention to their initialization.

SPIFFS is no longer special and it paves the way to adding new filesystems as libraries.
Ok, not entirely true: SPIFFS image building rules are still in the core Makefiles, this will be addressed in the future.

CL: Core refactoring: break out VFS and OTA into libs

PUBLISHED_FROM=0389aa29d78e9cc377315d2938889966c4bf143e

Author: Deomid Ryabkov

mos.yml

@@ -32,4 +32,4 @@ manifest_version: 2017-09-29
 
 # Temporary, while root manifest change propagates (2018/03/29).
 libs:
-  - origin: https://github.com/mongoose-os-libs/mongoose
+  - origin: https://github.com/mongoose-os-libs/core