xo-tokenizer: docs + error-handling improvement

drop exceptions for return-value error object

xo-tokenizer/docs/tokenizer-error-class.rst

@@ -0,0 +1,52 @@
+
+.. _tokenizer-error-class
+
+Tokenizer Error
+===============
+
+Represent a possible tokenizer error result, including parsing context
+
+Context
+-------
+
+.. ditaa::
+    :--scale: 0.85
+
+    +-----------------------------------------+----------+
+    |                tokenizer                |          |
+    +-----------------------------------------+          |
+    |               scan_result               |          |
+    +-----------------+-----------------------+  buffer  |
+    |     token       |cBLU tokenizer_error   |          |
+    +-----------------+-----------------------+          |
+    |    tokentype    |          span         |          |
+    +-----------------+-----------------------+----------+
+
+.. code-block:: cpp
+
+    #include <xo/tokenizer/tokenizer_error.hpp>
+
+Class
+------
+
+.. doxygenclass:: xo::scm::tokenizer_error
+
+Instance Variables
+------------------
+
+.. doxygengroup:: tokenizer-error-instance-vars
+
+Constructors
+------------
+
+.. doxygengroup:: tokenizer-error-ctors
+
+Access Methods
+--------------
+
+.. doxygengroup:: tokenizer-error-access-methods
+
+General Methods
+---------------
+
+.. doxygengroup:: tokenizer-error-general-methods