Merge branch 'feature/newlib_full_format' into 'master'

newlib: add "full" formatting support

This change adds support for 64-bit formats and C99 features to newlib printf/scanf functions. This support is enabled by default in menuconfig, but can be switched off to reduce code size.

Also adds missing functions such as fmod and fmodf.

- Fixes https://github.com/espressif/esp-idf/issues/52
- Fixes https://github.com/espressif/esp-idf/issues/83

See merge request !274