Update and add mmissing docstrings for sfdoc.sh

src/include-bash/sfdoc.sh

 
 shellfu import pretty
 
+#
+# Explore installed Shellfu modules
+#
+# Modules following Shellfu coding style[1] and installed at one of
+# directories listed by $SHELLFU_PATH can be listed and explored using
+# functions in this module.
+#
+#  [1]: https://github.com/AloisMahdal/shellfu/blob/master/notes/style.md
+#
+# Note that this module exists in order to allow developers implement commands
+# similar to sfdoc, which is preferred choice for normal use as it provides
+# more feature and better user experience.
+#
+
 #
 # Show hidden objects (modules, functions, variables)?
 #
+# An object (module, function or variable) is considered hidden if its name starts
+# with `_` (underscore).  These are ignored by default.  Set this to 'true' to show
+# them.
+#
 SFDOC_SHOW_HIDDEN=${SFDOC_SHOW_HIDDEN:-false}
 
 sfdoc__export() {
     #
-    # Export module doc as manpage
+    # Export docs of module $2 from file $3 as format $3
+    #
+    # Usage:
+    #
+    #     sfdoc__export FMT NAME PATH [ENCODING]
+    #
+    # Exports docs of module file at PATH, in format FMT, displaying
+    # NAME as "natural" name of the module.  Supported FMTs are
+    # 'manpage', 'markdown' and 'pod'.  ENCODING is currently used by
+    # 'pod' format only and is 'utf8' by default.
     #
     local format=$1             # format to export in
     local MName=$2              # name to use in headers
     #
     # List all objects of type $1 in module file $2
     #
+    # Usage:
+    #
+    #     sfdoc__ls TYPE PATH
+    #
+    # TYPE can be 'f' for functions or 'v' for variables.  PATH
+    # must be path to a module following Shellfu coding style
+    # (see DESCRIPTION section).
+    #
     local otype=$1
     local mpath=$2
     case $otype in
 
 sfdoc__ls_m() {
     #
-    # List all modules
+    # List all installed modules
+    #
+    # An installed module is a shell file named ending with '.sh' and
+    # placed in one of directories listed in comma-separated list
+    # in environment variable $SHELLFU_PATH.
     #
     shellfu _list_mfiles \
       | sed 's|\.sh$||; s|.*/||;' \