Dynamic alloc

This PR answers issue #10.

- You can run the test for SASIAE by running `./run_test.sh test` in `tests/sasiae/base/alloc`.
- You can run the test for AVR by running `make` in `tests/avr/base/alloc` and then by using your favourite UART communication tool (like minicom for example) to send an `S` to your board and wait for the result. It is not yet fully automatic because it seems like it hits a bug in Stream (you can take a look in `tests/avr/base/alloc/tester.cpp`, I kept the code)
- A static assertion is properly thrown if you try to use it on STM32.