textproc/lowdown: Unbreak by adding missing files to plist

While here, change MASTER_SITES and WWW to https.

Reported by:	poudriere build log
Approved by:	portmgr (unbreak)

textproc/lowdown/Makefile

@@ -3,7 +3,7 @@
 PORTNAME=	lowdown
 PORTVERSION=	0.4.1
 CATEGORIES=	textproc
-MASTER_SITES=	http://kristaps.bsd.lv/lowdown/snapshots/
+MASTER_SITES=	https://kristaps.bsd.lv/lowdown/snapshots/
 
 MAINTAINER=	bapt@FreeBSD.org
 COMMENT=	Simple Markdown translator

textproc/lowdown/pkg-descr

@@ -4,4 +4,4 @@ troff, or even mandoc(1). lowdown doesn't require XSLT, Python, or even Perl -
 it's just clean, secure, open source C code with no dependencies. Its
 canonical documentation is the lowdown(1) manpage.
 
-WWW: http://kristaps.bsd.lv/lowdown/
+WWW: https://kristaps.bsd.lv/lowdown/

textproc/lowdown/pkg-plist

@@ -5,11 +5,13 @@ lib/liblowdown.a
 man/man1/lowdown.1.gz
 man/man3/lowdown.3.gz
 man/man3/lowdown_buf.3.gz
+man/man3/lowdown_buf_diff.3.gz
 man/man3/lowdown_doc_free.3.gz
 man/man3/lowdown_doc_new.3.gz
 man/man3/lowdown_doc_parse.3.gz
 man/man3/lowdown_errstr.3.gz
 man/man3/lowdown_file.3.gz
+man/man3/lowdown_file_diff.3.gz
 man/man3/lowdown_html_free.3.gz
 man/man3/lowdown_html_new.3.gz
 man/man3/lowdown_html_rndr.3.gz