net/eternaltcp: Renamed to net/eternalterminal; Updated to 4.2.1

Request to rename:
https://github.com/MisterTea/EternalTCP/pull/92#issuecomment-368179461

Port changes:

• Updated GH_PROJECT/WWW accordingly
• Minor description correction

PR: 226231
Submitted by: Trevis <trevis@silencedpoet.com> (maintainer)
Approved by: tcberner (mentor, implicit)