parsers CHANGE redesign API of all the parsers

Simplify work with different inputs by introducing ly_in handler similar
to the printers' ly_out. The input handler can be used repeatedly and
also some input data manipulation functions are added.

Add new lys_parse() as a generic function using ly_in input handler. The
current API (lys_parse_* functions) was rewritten to be a wrapper of
the generic lys_parse().

Next to the unit tests for the parsers functions, also the similar tests
for printers functions are added.
diff --git a/tests/utests/schema/test_parser_yin.c b/tests/utests/schema/test_parser_yin.c
index 809bfd6..d2576b9 100644
--- a/tests/utests/schema/test_parser_yin.c
+++ b/tests/utests/schema/test_parser_yin.c
@@ -24,6 +24,7 @@
 #include "../../../src/common.h"
 #include "../../../src/tree_schema.h"
 #include "../../../src/tree_schema_internal.h"
+#include "../../../src/parser_internal.h"
 #include "../../../src/parser_yin.h"
 #include "../../../src/xml.h"
 #include "../../../src/xpath.h"