Added initial support for recursive expressions.

Updated docs and tests accordingly.

[SVN r54994]

test/regress/test_non_greedy_repeats.cpp

@@ -41,6 +41,5 @@ void test_non_greedy_repeats()
    TEST_REGEX_SEARCH("xx[/-]{0,2}?(?:[+-][0-9])??\\z", perl, "xx--", match_default, make_array(0, 4, -2, -2));
    TEST_INVALID_REGEX("a{1,3}{1}", perl);
    TEST_INVALID_REGEX("a**", perl);
-   //TEST_INVALID_REGEX("a++", perl);
 }