coreutils commands: move pages to common/ folder (#2442)

pages/common/unexpand.md

@@ -0,0 +1,23 @@
+# unexpand
+
+> Convert spaces to tabs.
+
+- Convert blanks in each file to tabs, writing to standard output:
+
+`unexpand {{file}}`
+
+- Convert blanks to tabs, reading from standard output:
+
+`unexpand`
+
+- Convert all blanks, instead of just initial blanks:
+
+`unexpand -a {{file}}`
+
+- Convert only leading sequences of blanks (overrides -a):
+
+`unexpand --first-only {{file}}`
+
+- Have tabs a certain number of characters apart, not 8 (enables -a):
+
+`unexpand -t {{number}} {{file}}`