[WIP][Docs] Add documentation for ENI types.

docs/404.rst

@@ -0,0 +1 @@
+This section does not exist yet. `(´-ι_-\`)`

docs/documentation.rst

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+=============
+Documentation
+=============
+
+.. toctree::
+   :maxdepth: 2
+
+   types

docs/index.rst

@@ -13,4 +13,5 @@ Contents
 
    getting-started
    developer-guide
+   documentation
    contributing

docs/types.rst

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+=====
+Types
+=====
+
+ENI Types
+---------
+
+.. _types-eni-int:
+
+ENI Integers
+````````````
+
+All integer types in ENI is implemented using `boost::multiprecision::number <boostnumber_>`__.
+Some of them are aliases for types predefined in `boost::multiprecision::cpp_int <boostcppint_>`__.
+
++---------------+-------------+--------+------------------------------+
+| Integer Type  | Size (bits) | Signed | Note                         |
++===============+=============+========+------------------------------+
+| ``eni::s256`` | 256         | ✔      |                              |
++---------------+-------------+--------+------------------------------+
+| ``eni::Int``  | 256         | ✔      | Alias for ``eni::s256``.     |
++---------------+-------------+--------+------------------------------+
+| ``eni::u256`` | 256         | ✘      |                              |
++---------------+-------------+--------+------------------------------+
+| ``eni::u160`` | 160         | ✘      | Size of an Ethereum address. |
++---------------+-------------+--------+------------------------------+
+| ``eni::u128`` | 128         | ✘      |                              |
++---------------+-------------+--------+------------------------------+
+| ``eni::u64``  | 64          | ✘      |                              |
++---------------+-------------+--------+------------------------------+
+| ``eni::UInt`` | 256         | ✘      | Alias for ``eni::u256``.     |
++---------------+-------------+--------+------------------------------+
+
+Operations on ENI Integers
+''''''''''''''''''''''''''
+
+See `the documentation for boost::multiprecision::number <boostnumber_>`__ for
+supported operations.
+
+You may use `boost::lexical_cast <boostlexcast_>`__ to convert ENI integers to strings.
+
+.. _boostnumber: https://www.boost.org/doc/libs/1_58_0/libs/multiprecision/doc/html/boost_multiprecision/ref/number.html
+.. _boostcppint: https://www.boost.org/doc/libs/1_58_0/libs/multiprecision/doc/html/boost_multiprecision/tut/ints/cpp_int.html
+
+.. _boostlexcast: https://www.boost.org/doc/libs/1_58_0/doc/html/boost_lexical_cast.html
+
+Suggested Use of ENI Integers
+'''''''''''''''''''''''''''''
+
+.. include:: 404.rst
+
+.. _types-eni-bool:
+
+ENI Boolean
+```````````
+
+``eni::Bool`` is an alias for C++ ``bool``.
+
+.. _types-eni-addr:
+
+ENI Address
+```````````
+
+``eni::Address`` is an alias for ``eni::u160`` (20 bytes, size of an Ethereum address).
+
+.. _types-json:
+
+JSON Types
+----------
+
+.. include:: 404.rst