add the pure bash core: core, str, naming and tags

Ported from make/utils.mk, make/def.mk, make/apps/def.docker.mk and
make/apps/def.mk, with the examples that sat as dead comments in
make/apps/def.mk turned into actual assertions.

Two deviations from the make macros are pinned and documented in DELTAS.md;
both only show up on code paths nothing uses.

lib/str.sh

@@ -0,0 +1,33 @@
+#shellcheck shell=sh
+# str: string helpers ported from make/utils.mk and make/def.mk.
+
+# myos_lower STRING / myos_upper STRING
+myos_lower() { printf '%s' "$1" | tr '[:upper:]' '[:lower:]'; }
+myos_upper() { printf '%s' "$1" | tr '[:lower:]-.' '[:upper:]__'; }
+
+# myos_name STRING  compose-project-safe name: lowercase, no . - _
+# (make: $(subst _,,$(subst -,,$(subst .,,$(call LOWERCASE,$(1))))))
+myos_name() { printf '%s' "$1" | tr '[:upper:]' '[:lower:]' | tr -d '._-'; }
+
+# myos_slugify STRING  keep [a-z0-9_], everything else becomes _
+myos_slugify() { printf '%s' "$1" | tr '[:upper:]' '[:lower:]' | sed 's/[^a-z0-9_]/_/g'; }
+
+# myos_reverse WORDS...  reverse the order of space separated words
+myos_reverse() {
+  _out=
+  for _w in $1; do _out="$_w${_out:+ }$_out"; done
+  printf '%s' "$_out"
+}
+
+# myos_verle A B  true when version A <= B (make: verle)
+myos_verle() {
+  [ -n "$1" ] || return 1
+  [ -n "$2" ] || return 1
+  [ "$1" = "$(printf '%s\n%s\n' "$1" "$2" | sort -V | head -n1)" ]
+}
+
+# myos_verlt A B  true when version A < B
+myos_verlt() {
+  [ "$1" = "$2" ] && return 1
+  myos_verle "$1" "$2"
+}