Use Make to build binaries
Add back build.sh

Need the shell script for Docker build
Simplified Makefile
DRY Makefile according to @tianon's suggestion
Streamlined the complete building process

The Makefile will handle native build, cross compiling, and Docker build
as well. Also updated the README to reflect the changes.
Fixed typo in README
`make` default to Docker build
Merge pull request #88 from riobard/Makefile

Use Make to build binaries