massively improved build system

ax_check_qt.m4

@@ -1,6 +1,10 @@
 # SYNOPSIS
 #
-#   AX_CXX_CHECK_QT([qt_prefix], [list-of-qt-modules], [optional-modules])
+#   Check if a module exists:
+#     AX_CXX_CHECK_QT([qt_prefix], [list-of-qt-modules], [optional-modules])
+#
+#   Abort if a module does not exist:
+#     AX_CXX_REQUIRE_QT([qt_prefix], [list-of-qt-modules], [optional-modules])
 #
 # DESCRIPTIONS
 #
@@ -32,6 +36,7 @@
 #      exist only in Qt5, but not in Qt4, such as QtWidgets or
 #      QtWebKitWidgets
 
+
 AC_DEFUN([AX_CXX_QT_TOOL], [
   if test -z "$HAVE_$1"; then
     HAVE_$1=1
@@ -146,6 +151,40 @@ qrc_%.cxx: %.qrc
   AC_SUBST(AX_ADDITIONAL_QT_RULES_HACK)
 ])
 
+# SYNOPSIS
+#
+#   AX_CXX_CHECK_QT([qt_prefix], [list-of-qt-modules], [optional-modules])
+#
+# DESCRIPTIONS
+#
+#    qt_prefix
+#
+#      Each call to AX_CXX_CHECK_QT should have a different prefix
+#      value (with a few exceptions discussed later on). This value,
+#      usually provided in uppercase, is used as prefix to the
+#      variables holding the compiler flags and libraries reported by
+#      pkg-config.
+#
+#      For instance, if your prefix was to be FOO you'll be provided
+#      two variables FOO_CFLAGS and FOO_LIBS.
+#
+#      This will also be used as message during the configure checks:
+#      checking for FOO....
+#
+#    list-of-modules
+#
+#      A single call to the macro can check for the presence of one or
+#      more qt modules; you'll see later how to make good use of this
+#      feature. Each entry in the list can have a version comparison
+#      specifier, with the same syntax as the Requires keyword in the
+#      data files themselves.
+#
+#    optional-modules
+#
+#      Optional list of more, optional modules, e.g. modules that
+#      exist only in Qt5, but not in Qt4, such as QtWidgets or
+#      QtWebKitWidgets
+
 AC_DEFUN([AX_REQUIRE_QT], [
   AX_CHECK_QT([$1], [$2], [$3])
   if ! test "$HAVE_$1" -eq 1; then