add ebuilds (with some appropriate code change)

ebuild/sci-libs/libsla/Manifest

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+EBUILD libsla-7.0.0.ebuild 646 BLAKE2B 4e98c6bcc7a5c327ba2f7c936f4e77df0b6872debe04965a291c454464f6f1efc730d41e864e9547b7026f3777e5e01881d145c6857e0c24547cbf1e4f958392 SHA512 37b02e5adfe34ae0bdf0b5b76539fb7f944a4b974af7da99cc32f6c80e1620041d334bbd7d6486afd994080acd1d9ac1c377a9f8bbcd990c22aab6bd378b029d

ebuild/sci-libs/libsla/libsla-7.0.0.ebuild

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+# Copyright 1999-2018 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=6
+
+inherit unpacker
+
+DESCRIPTION="Old SLA astronomy calculations library. DEPRECATED! Don't use it in new projects. Use libnova or libsofa instead."
+HOMEPAGE=""
+SRC_URI=""
+
+LICENSE="GPL-3"
+SLOT="0"
+KEYWORDS="amd64 x86"
+IUSE=""
+
+DEPEND=""
+RDEPEND="${DEPEND}"
+S="${WORKDIR}"
+
+src_unpack() {
+    cp -r /home/eddy/C-files/apogee_control/slalib/* ${S} || die
+}
+
+
+src_install() {
+    insinto /usr/local/lib
+    doins libsla.so
+    insinto /usr/local/include
+    doins slalib.h  slamac.h
+    insinto /usr/share/pkgconfig
+    doins sla.pc
+}