scripts optimization

scripts.mk is called for each .mk file.
*.mk files are optimized with only:
 [bin|lib|slib]-y+=<target name>
 <target name>_SOURCES:=<source file>
 <target name>_CFLAGS:=<CFLAGS for target>
 <target name>_LDFLAGS:=<LDFLAGS for target>
 <target name>_LIBRARY:=<libraries list for target>
each *.mk has to be inside the source directory
scripts allows to install package files

installation is done with the use of:
 BINDIR for <bin-y> files
 LIBDIR for <dlib-y> and <lib-y> files
 PKGLIBDIR for <modules-y> files
 DATADIR for <data-y> files

DESTDIR is added if exited