Add Ubuntu -> Linux-on-ARM sample CMake toolchain files

Add separate sample CMake toolchain files targeting Linux running
on ARM, with and without hardware floating point support. Samples
use the `gcc-arm-linux-gnueabihf` and `gcc-arm-linux-gnueabi` cross
toolchains from the standard Ubuntu package repositories.

Added Math.sqrt() that was missing in math.c, and added relevant test case

Merge branch 'jf/parser-dump' of https://github.com/thecodeshop/mruby into thecodeshop-jf/parser-dump

Improve Time

remove mrb_open NULL check for small test programs.  They are only for proof-on-concept test, not production code.  Adding precise checks are not needed for those code

guard mrb_open mem allocation and downstream usage

Class#superclass improvement

A rescue clause with no parameter list rescues only StandardErrors