Add default values to arch and platform

[malept]

Have you read the section in CONTRIBUTING.md about pull requests?

Yes

Summarize your changes:

The defaults are the host's arch and platform values.

Fixes #36.

Are your changes appropriately documented?

Updated NEWS, readme, API, & CLI docs. I probably need to update the readme as well (have not done that yet).

Do your changes have sufficient test coverage?

Changed the defaults test to test the new platform/arch defaults.

Does the testsuite pass successfully on your local machine?

Yes

[malept]

@kevinsawicki @jlord @zeke any comments/concerns you have on either the concept or the changes would be much appreciated. This one is likely going to be a fairly controversial change.

[kevinsawicki]

any comments/concerns you have on either the concept or the changes would be much appreciated.

My instinct is to keep 32-bit as the default arch instead of the host arch (which is presumably 64-bit since developers commonly use 64-bit machines). When unspecified, I'm assuming the person wants a package that will work on the most machines possible, and 32-bit will work more places than 64-bit.

For platform though, the host platform sounds like a great default that people will expect 👍

[malept]

My rationale for making both defaults the same as the host is that it is easier for the developer to test. (I should have put that in the PR summary.)

I believe that Windows 32-bit executables will run on 64-bit machines (maybe? I could be wrong) but in order for Linux 32-bit executables to run, the whole 32-bit glibc/etc stack also needs to be installed (e.g., dpkg --add-architecture i386), unless for some reason Electron is statically linked to musl or similar 😄

[kevinsawicki]

I believe that Windows 32-bit executables will run on 64-bit machines

Yup, that is my understanding as well.

but in order for Linux 32-bit executables to run, the whole 32-bit glibc/etc stack also needs to be installed (e.g., dpkg --add-architecture i386)

Oh, interesting, didn't realize this.

Since it seems like the better default on Linux is the host arch, and their is no 32-bit on macOS, the host arch is the better default.

One question, if I am on 32-bit Linux and Windows, and I request to build for macOS with no arch specified, will it still build a 64-bit version of mac since their is no 32-bit, or would it error about 32-bit mac being unavailable?

[malept]

One question, if I am on 32-bit Linux and Windows, and I request to build for macOS with no arch specified, will it still build a 64-bit version of mac since their is no 32-bit, or would it error about 32-bit mac being unavailable?

It will currently error. It would also error if #106 is fixed and you only specify --arch=armv7l on OSX/Windows.

[zeke]

Nice! Are you planning to land this in 8.0.0?

[malept]

Yup!