Clarify error logging around exe download in extractProtoc

[clairemcginty]

from extractProtoc:

protoc-jar/src/main/java/com/github/os72/protocjar/Protoc.java

Lines 199 to 223 in ced740f

	File exeFile = null;
	if (protocVersion.mArtifact == null) { // look for embedded protoc and on web (maven central)
	// look for embedded version
	String srcFilePath = "bin/" + protocVersion.mVersion + "/" + getProtocExeName(protocVersion);
	try {
	File protocTemp = new File(binDir, "protoc.exe");
	populateFile(srcFilePath, protocTemp);
	log("embedded: " + srcFilePath);
	protocTemp.setExecutable(true);
	protocTemp.deleteOnExit();
	return protocTemp;
	}
	catch (FileNotFoundException e) {
	//log(e);
	}
	// look in cache and maven central
	exeFile = findDownloadProtoc(protocVersion);
	}
	else { // download by artifact id from maven central
	String downloadPath = protocVersion.mGroup.replace(".", "/") + "/" + protocVersion.mArtifact + "/";
	exeFile = downloadProtoc(protocVersion, downloadPath, true);
	}
	if (exeFile == null) throw new FileNotFoundException("Unsupported platform: " + getProtocExeName(protocVersion));

I've occasionally seen transient issues with Maven downloads/caching that result in exeFile being evaluated to null -- but the error message is always "Unsupported platform", which isn't always accurate. I think having a bit more specific logging on which step actually failed would be really helpful.

[os72]

Ack, thanks
(Please note I need to limit the time I dedicate to this project. Would you / your employer consider sponsoring/donating?)

[clairemcginty]

@os72, coming back to this issue, would you be open to introducing a logging lib (slf4j or JUL) into this repo? that way we could replace some of the commented-out log(...) calls in the code with a Logger#debug, and the user could specify how noisy they'd like log output to be.

I understand wanting to keep the repo vanilla Java though

[os72]

Would your employer consider supporting this project?