Allow transient compilation, without touching the file system

[trieloff]

• instead of forcing to write a file, introduces a new compileTransient method, which returns a string

[tripodsan]

basically ok, but I don't like the name transient.
other options:

• just return the string in the normal compile function and handle the save somewhere else
• maybe add compileToFile()

[tripodsan]

btw, why would this fix adobe/parcel-plugin-htl#1 ?

[trieloff]

I didn't want to break compatibility for compile. I can change the name of transientCompile into compileToString, add a compileToFile and make compile an alias for compileToFile

[tripodsan]

I didn't want to break compatibility for compile.
but then we never evolve the API if we already care about backward compatibility. :-)

never mind... we will clean it up eventually. the compile should anyways be async and return a promise....