Playpen Sans: Version 1.001 added (#6746)

* [gftools-packager] Playpen Sans: Version 1.001 added

* Playpen Sans Version 1.001 taken from the upstream repo https://github.com/TypeTogether/Playpen-Sans at commit https://github.com/TypeTogether/Playpen-Sans/commit/de384a1c4e7fd55f020dedeba4a87740d4ad6ef1.

* Small fixes to DESCRIPTION.en_us.html

* DESCRIPTION.en_us.html url fix

* METADATA.pb symbols subset + stroke added

* METADATA.pb subsets fix

* METADATA.pb: `math` subsetting added