update for PSR-4
Merge pull request #28 from triplepoint/feature/update-for-psr4

update for PSR-4
revise unit of measure construction, clean up quantity classes.
fix instances of 'use \' according to php standards
psr standards
dropping php 5.3 support over the 'callable' typehint
expanded the readme a bit
make failing php 5.6 tests not optional.  Bump phpunit dependency version.  fix weird travis phpunit call
replace array() with [].  Fix a logic mistake in naming the fromNativeUnitFactor variable.
updated README for readability
general cleanup
remove references to gitapidoc.com
add notes for v1.2.0 to the changelog
Merge upstream changes

Conflicts:
	source/PhpUnitsOfMeasure/PhysicalQuantity/Length.php
	source/PhysicalQuantity/ElectricCurrent.php