Don't increment the counter when a button is pressed
Use -Os for CC2538 builds

As discussed in #503, -Os was broken with one of the toolchains
recommended in the platform's README and for that reason we were
using -O2 by default.

This commit sets the default to -Os and updates the README to no
longer recommend the toolchain in question
Make some CC2538 CFLAGS and LDFLAGS common

Some CFLAGS and LDFLAGS previously only enabled with SMALL=1 have
now been enabled for all builds, regardless of the value of SMALL.

Therefore, from now on, SMALL only chooses between -Os and -O2
Merge pull request #549 from g-oikonomou/cc2538-code-size-opt

Improve optimisation settings for CC2538 builds
Avoid compiler warnings.
Merge pull request #550 from oliverschmidt/master

Avoid compiler warnings.
Merge pull request #493 from g-oikonomou/cc2538-demo-example-counter

Don't increment the counter when a button is pressed
Some fine tuning after the recent general modularization.
Some fine tuning after the recent general modularization.
Merge pull request #553 from oliverschmidt/master

Some fine tuning after the recent general modularization.
Fixed win32 broken by recent changes.
Merge pull request #554 from oliverschmidt/master

Fixed win32 broken by recent changes.