Small typo, can lead to copy and paste fails

Signed-off-by: Joseivaldo Benito Junior <jrbenito@benito.qsl.br>
Merge pull request #247 from jrbenito/master

Fix a typo in README
Allow libraries/sketches to have the same name as system libs,
e.g. main or Wire

Doesn't seem to work with main.cpp but main.ino works.

Fixes issue #229 and #244
Added *.cpp to extensions supported by "make generate_assembly"