fixed `build` to `main`

Minor typo in instructions
`build` to `main`

Minor instruction error in README
Merge pull request #333 from kennethlimcp/patch-4

fixed `build` to `main`
typo "testes" --> "tests"
Merge pull request #335 from kennethlimcp/patch-2

typo "testes" --> "tests"
Bug fix : syshealth_hal functions now compiles for specified platform
Merged in #328 to feature/hal, and added GCC_ARM_PATH for embedXCode.
merged PR #323 (dfu-suffix) into feature/hal
support for having application sources outside the firmware folder.
typo in spark_wiring_random.h  min -> max
changed ci core to mat's core for easier debugging failed builds
ensure target file is unique for each test suite, so each suite is correctly built.
info message to know which core is being used for the ci-memory-test
WLAN ping tests fail when driven from travis-ci, but work fine with exactly the same image running locally. The cloud operations are somehow interfering with ping.  Sleeping these tests until we can snoop for a fix.
test excludes to make ci-build pass until we can properly create the needed test fixtures.
fix for including/excluding tests in test_setup.sh. test.include files need to have a final blank line.
moved core-v1/testapp2 to core-v1-fixture1/testapp2 since this requires a different hardware fixture compared to the standard test suite.
tests in platforms with no assigned core are skipped. The new core-v1-fixture platform is skipped until we have a core that is setup with the required fixture.
moved newlib_stubs.cpp from main to hal
removed LIBS def from wiring. (Modules don't export their libs - importing modules identify them by name.)