Token bug in converter.m #35

Both the GitHub and GitLab cases pass "" as the default token (lines 21, 25), but the GitHub.m and GitLab.m constructors expect missing to skip authentication. So even when no token env var is set, "" gets sent as the auth header and the API returns 401. The unauthenticated GitHub path should work but can't because of this.

Reproduction Steps:

1. Install DocMaker v0.8.0 (MATLAB_DocMaker.mltbx from the GitHub release) in MATLAB:

>> matlab.addons.install("MATLAB_DocMaker.mltbx")

2. Make sure no token is set anywhere:

>> setenv("DOCMAKER_GITLAB_HOSTNAME", "")
>> setenv("DOCMAKER_GITLAB_TOKEN", "")

3. Minimal repro:

>> setenv("DOCMAKER_CONVERTER", "GitHub")
>> c = docmaker.converter();
>> c.Token % Expected <missing>

ans = 

    ""

>> c.md2xml("# Hello")
Error using docmaker.GitHub/md2xml (line 80)
[HTTP/1.1 401 Unauthorized] Bad credentials