Fix size_t not found (#46)

* Include stddef in AbstractList
* Bump version to 3.0.1

Version 3.0.0 (#42)

Fix mutability

rename doxygen project number

Improvements and additions for 2.1.4 (#36)

- improve "add" functions to handle rvalues
- add sort (quicksort)
- add fromArray
- add != operator
- add + operator for rvalues

fix platformio library json

fix frameworks

remove if statement because fix was deployed in: adafruit/ci-arduino#131

Merge pull request #16 from nkaaf/road_to_2_1_0

PR for 2.1.0

Merge pull request #8 from nkaaf/change_default_mutability_behavior

change default mutable state; small rework on getting values/pointers