Support for ESP32C3 (RISC-V)

• New platform define __ESP32_RISC__ for ESP32C3 RISC-V based chips, e.g. Adafruit QTPY ESP32C3.
  Note: while legacy ESP32 with Tensilica cores default to SPIFFS filesystem, the new ESP32C3 with RISC-V default to LittleFS.

Small doc fixes

Doc fixes for USTD_FEATURE_MEMORY.

LittleFS support for ESP32

News ESP32 now support LittleFS too.
For compatibility reasons, ESP32 currently defaults to SPIFFS.
Use #define USTD_OPTION_FS_FORCE_LITTLEFS to use LittleFS with ESP32.

Teensy 4.0 support

Support for __TEENSY40__ platform define.
Fixes #20 , thanks @SteveEisner

Do not mutate (extend) arrays on read

Based on #17 , thanks @mzanetti

Before 0.7.0 an array could extend via a read operation.
This has been changed: arrays are never mutated by reads.

Inline global operators and functions

Based on #13, @mo22:
Use inline to allow multiple inclusions of global operators (new) and functions within one sub-project.

RP2040 support

0.6.1 (2021-02-26) Initial Raspberry PICO rp2040 support.

More platforms, iterator and copy-constructor support for map, queue and array

0.6.0 (2021-02-09) New platforms, iterator and copy-constructor support.

• Support for iterators and copy-constructors in ustd::array, ustd::queue, and ustd::map.
  (Thanks @proddy for iterator sample implementation, fixes #4 .)
• Platforms: Feather M4 added: __FEATHER_M4__
• Blackpill STM32F411 added.
• Arduino Nano 33 BLE added. Note: requires platformio's lib_ldf_mode = chain+ definition
  in platform.ini, otherwise platformio will get confused about including WiFi.h, because
  of faulty #ifdef parsing of ustd_platformio.h.
• ASSERT() macros removed due to clashes.

Breaking rename of includes: new prefix `ustd_` to avoid conflicts

0.5.0 (2021-01-30) BREAKING CHANGE:

In order to prevent name-clashes for include-files for Arduino-IDE users, all
ustd include files now have an ustd_ prefix. Compatibility-versions without ustd_ that
include the ustd_ versions are provided, with exception of queue.h (clash with ESP8266-Wifi) and
platform.h (clash with RISC-V sdk).

Missing UST_FEATURE_FILESYSTEM added for ESPs

• UST_FEATURE_FILESYSTEM was not defined for __ESP__ and __ESP32__
• Note: 0.4.3 was skipped because that was already (incorrectly) used in library.json of 0.4.2.