Introduce three options:
1. SNOWHOUSE_IS_CPP11 replaces 'cfg' variable as this is what it was being used for. Default OFF.
2. SNOWHOUSE_BUILD_TESTS to allow for optional building of the Snowhouse tests. Default ON.
3. SNOWHOUSE_RUN_TESTS to allow for optional running of the Snowhouse tests. Default ON. Dependent on SNOWHOUSE_BUILD_TESTS.

Updated cross_compile.sh to reflect the change in 'cfg' variable.
Introduce three options:
1. SNOWHOUSE_IS_CPP11 replaces 'cfg' variable as this is what it was being used for. Default OFF.
2. SNOWHOUSE_BUILD_TESTS to allow for optional building of the Snowhouse tests. Default ON.
3. SNOWHOUSE_RUN_TESTS to allow for optional running of the Snowhouse tests. Default ON. Dependent on SNOWHOUSE_BUILD_TESTS.

Updated cross_compile.sh to reflect the change in 'cfg' variable.
Merge pull request #4 from andystanton/feature/add-options

Make snowhouse tests optional