migrate fully to meson build system

- drop old build system
- move shared include and source files to common directory
- drop "rc-" prefix from shared include and source files
- move executable-specific code to individual directories under src
- adjust top-level .gitignore file for new build system

This closes #489.

pkgconfig/.gitignore

@@ -1,2 +0,0 @@
-einfo.pc
-openrc.pc

pkgconfig/Makefile

@@ -1,12 +0,0 @@
-DIR=	${PKGCONFIGDIR}
-SRCS=	einfo.pc.in openrc.pc.in
-INC=	einfo.pc openrc.pc
-
-.DEFAULT:
-	${SED} -n -e 's/^VERSION=[[:space:]]*\([^[:space:]]*\).*/#define VERSION "\1${GITVER}\"/p' ../../Makefile > version.h
-
-SED_EXTRA=	-e 's:@VERSION@:${VERSION}:g'
-
-MK=	../mk
-include ../Makefile.inc
-include ${MK}/scripts.mk