Add a command to amalgamate one or multiple build scripts

[yungyuc]

The build script files under scripts/build.d/ cannot run without the full source tree of devenv. Therefore we cannot build the dependency packages by simply copying the build scripts.

I would like to propose to add an enhancement feature to amalgamate a build script with the shared bash code. By amalgamation, it is like how rapid yaml creates a single header file or how sqlite creates the single C file. But for devenv the amalgamation creates a single bash script rather than a source file for compiler.

With the amalgamation, we may replace the hand-crafted build script with a devenv-generated one.