Update Makefile

[b-]

Added export PATH := $(DEVKITARM)/bin:$(PATH) from the CakesROPSpider Makefile. This solves some compilation issues I was having on OS X 10.11 El Capitan.

Also added .DEFAULT_GOAL := release which will allow running make without arguments to build rxTools

[b-]

The path issues I was having are probably user error on my part, but CakesROPSpider's Makefile still prevents such user errors as long as $DEVKITARM is defined properly. By adding this line to the main rxTools Makefile we're actually ensuring that $DEVKITARM/bin is the first folder in the command search path, which means that anybody with a properly installed copy of devkitARM needn't add it to their path variable for compilation.

Also, the fact that compiling requires make release was getting annoying to me, since most Makefiles I've encountered have a sane default target. By listing all-target-brahma in the Makefile as the first target whose name doesn't begin with a . (e.g., .PHONY — what is that anyway?) it was the only target that would be compiled upon simply typing make, requiring a user to type make release to properly compile rxTools. .DEFAULT_GOAL is a Makefile variable pointing to what the default target should be (in this case, release).