/adds builtinvalues to vyper.vim

[githubsands]

Adds missing values sha256, pow_mod256, and empty for built in functions to vyper

Source sha256:

.. py:function:: pow_mod256(a: uint256, b: uint256) -> uint256

    Return the result of ``a ** b % (2 ** 256)``.

    This method is used to perform exponentiation without overflow checks.

    .. code-block:: python

        @external
        @view
        def foo(a: uint256, b: uint256) -> uint256:
            return pow_mod256(a, b)

    .. code-block:: python

        >>> ExampleContract.foo(2, 3)
        8
        >>> ExampleContract.foo(100, 100)
        59041770658110225754900818312084884949620587934026984283048776718299468660736

Source pow_mod256:

.. py:function:: sha256(_value) -> bytes32

    Return a ``sha256`` (SHA2 256-bit output) hash of the given value.

    * ``_value``: Value to hash. Can be a literal string, ``Bytes``, or ``bytes32``.

    .. code-block:: python

        @external
        @view
        def foo(_value: Bytes[100]) -> bytes32
            return sha256(_value)

    .. code-block:: python

        >>> ExampleContract.foo(b"potato")
        0xe91c254ad58860a02c788dfb5c1a65d6a8846ab1dc649631c7db16fef4af2dec

Source empty:

.. py:function:: empty(typename) -> Any

    Return a value which is the default (zero-ed) value of its type. Useful for initializing new memory variables.

    * ``typename``: Name of the type

    .. code-block:: python

        @external
        @view
        def foo():
            x: uint256[2][5] = empty(uint256[2][5])