Add custom import function mkit_import()

To minimize code needed to import a module

src/include/build.sh

 #!/bin/bash
 
-. "$MKIT_DIR/include/ini.sh"   || die "cannot import ini.sh"
-. "$MKIT_DIR/include/facts.sh" || die "cannot import facts.sh"
+mkit_import ini
+mkit_import facts
 
 
 _build1() {

src/include/facts.sh

 #!/bin/bash
 
-. "$MKIT_DIR/include/ini.sh" || die "cannot import ini.sh"
+mkit_import ini
 
 git_bool() {
     #

src/include/mkit.sh

 #!/bin/bash
 
-. "$MKIT_DIR/include/build.sh"  || die "cannot import build.sh"
-. "$MKIT_DIR/include/deploy.sh" || die "cannot import deploy.sh"
-. "$MKIT_DIR/include/release.sh" || die "cannot import release.sh"
-. "$MKIT_DIR/include/ini.sh"    || die "cannot import ini.sh"
+die() {
+    #
+    # Exit with message and non-zero exit status
+    #
+    echo "fatal: $*" >&2
+    exit 4
+}
+
+mkit_import() {
+    #
+    # Import mkit module $1.sh
+    #
+    # Check for module, source it and die with reasonable message if needed.
+    #
+    local modname=$1
+    local modpath
+    modpath="$MKIT_DIR/include/$modname.sh"
+    test -f "$modpath" || die "no such module: $modpath"
+    bash -n "$modpath" || die "bad syntax: $modpath"
+    #shellcheck disable=SC1090
+    . "$modpath" || die "failed to import: $modname"
+}
+
+mkit_import build
+mkit_import deploy
+mkit_import release
+mkit_import ini
 
 _valid_targets() {
     #
     done
 }
 
-die() {
-    #
-    # Exit with message and non-zero exit status
-    #
-    echo "fatal: $*" >&2
-    exit 4
-}
-
 _compver() {
     #
     # True if version $1 matches our version

src/include/release.sh

 #!/bin/bash
 
-. "$MKIT_DIR/include/ini.sh"   || die "cannot import ini.sh"
-. "$MKIT_DIR/include/facts.sh" || die "cannot import facts.sh"
+mkit_import ini
+mkit_import facts
 
 _bump_version() {
     #