devel/flexjson: Update to 2.1

amutu@amutu.com took maintainership.

Additional port changes:

• DISTVERSION
• Update of MASTER_SITES.
• No need for USES=zip any more.
• No need for NO_WRKSUBDIR.
• Minor change in do-install.
• PORTDOCS to the end.

PR: 220075
Submitted by: Jov <amutu@amutu.com>
Approved by: tcberner (mentor, implicit)