Emitter: Output space after an alias mapping key (#185)

Before:
    a: &b x
    *b: c

Now:
    a: &b x
    *b : c

Passing tests:
* 26DV: Whitespace around colon in mappings
* E76Z: Aliases in Implicit Block Mapping
* X38W: Aliases in Flow Objects

Test manually because `make test-suite` will overwrite changes in the skiplist:

    ./tests/run-parser-test-suite tests/run-test-suite/data/26DV/in.yaml | ./tests/run-emitter-test-suite
    ./tests/run-parser-test-suite tests/run-test-suite/data/E76Z/in.yaml | ./tests/run-emitter-test-suite
    ./tests/run-parser-test-suite tests/run-test-suite/data/X38W/in.yaml | ./tests/run-emitter-test-suite

Or edit tests/run-test-suite/test/blacklist/libyaml-emitter and do:

    (cd tests/run-test-suite; prove -lv test)

Also I added some newlines to yaml.h to help identifying states by number.

include/yaml.h

@@ -1020,6 +1020,7 @@
     YAML_PARSE_DOCUMENT_CONTENT_STATE,
     /** Expect DOCUMENT-END. */
     YAML_PARSE_DOCUMENT_END_STATE,
+
     /** Expect a block node. */
     YAML_PARSE_BLOCK_NODE_STATE,
     /** Expect a block node or indentless sequence. */
@@ -1030,6 +1031,7 @@
     YAML_PARSE_BLOCK_SEQUENCE_FIRST_ENTRY_STATE,
     /** Expect an entry of a block sequence. */
     YAML_PARSE_BLOCK_SEQUENCE_ENTRY_STATE,
+
     /** Expect an entry of an indentless sequence. */
     YAML_PARSE_INDENTLESS_SEQUENCE_ENTRY_STATE,
     /** Expect the first key of a block mapping. */
@@ -1040,6 +1042,7 @@
     YAML_PARSE_BLOCK_MAPPING_VALUE_STATE,
     /** Expect the first entry of a flow sequence. */
     YAML_PARSE_FLOW_SEQUENCE_FIRST_ENTRY_STATE,
+
     /** Expect an entry of a flow sequence. */
     YAML_PARSE_FLOW_SEQUENCE_ENTRY_STATE,
     /** Expect a key of an ordered mapping. */
@@ -1051,6 +1054,7 @@
     /** Expect the first key of a flow mapping. */
     YAML_PARSE_FLOW_MAPPING_FIRST_KEY_STATE,
     /** Expect a key of a flow mapping. */
+
     YAML_PARSE_FLOW_MAPPING_KEY_STATE,
     /** Expect a value of a flow mapping. */
     YAML_PARSE_FLOW_MAPPING_VALUE_STATE,
@@ -1489,6 +1493,7 @@
     YAML_EMIT_DOCUMENT_CONTENT_STATE,
     /** Expect DOCUMENT-END. */
     YAML_EMIT_DOCUMENT_END_STATE,
+
     /** Expect the first item of a flow sequence. */
     YAML_EMIT_FLOW_SEQUENCE_FIRST_ITEM_STATE,
     /** Expect an item of a flow sequence. */
@@ -1499,6 +1504,7 @@
     YAML_EMIT_FLOW_MAPPING_KEY_STATE,
     /** Expect a value for a simple key of a flow mapping. */
     YAML_EMIT_FLOW_MAPPING_SIMPLE_VALUE_STATE,
+
     /** Expect a value of a flow mapping. */
     YAML_EMIT_FLOW_MAPPING_VALUE_STATE,
     /** Expect the first item of a block sequence. */
@@ -1509,6 +1515,7 @@
     YAML_EMIT_BLOCK_MAPPING_FIRST_KEY_STATE,
     /** Expect the key of a block mapping. */
     YAML_EMIT_BLOCK_MAPPING_KEY_STATE,
+
     /** Expect a value for a simple key of a block mapping. */
     YAML_EMIT_BLOCK_MAPPING_SIMPLE_VALUE_STATE,
     /** Expect a value of a block mapping. */

src/emitter.c

@@ -1023,6 +1023,8 @@
 {
     if (!yaml_emitter_process_anchor(emitter))
         return 0;
+    if (emitter->simple_key_context)
+        if (!PUT(emitter, ' ')) return 0;
     emitter->state = POP(emitter, emitter->states);
 
     return 1;