Swish operation specification (#1200)

* Add Swish operation specification

docs/ops/activation/Swish_4.md

@@ -0,0 +1,53 @@
+## Swish <a name="Swish"></a>
+
+**Versioned name**: *Swish-4*
+
+**Category**: *Activation*
+
+**Short description**: Swish takes one input tensor and produces output tensor where the Swish function is applied to the tensor elementwise.
+
+**Detailed description**: For each element from the input tensor calculates corresponding
+element in the output tensor with the following formula: 
+
+    \f[
+    Swish(x) = x / (1.0 + e^{-(beta * x)})
+    \f]
+
+The Swish operation is introduced in the [article](https://arxiv.org/pdf/1710.05941.pdf).
+
+**Attributes**:
+
+**Inputs**:
+
+*   **1**: Multidimensional input tensor of type *T*. **Required**.
+
+*   **2**: Scalar with non-negative value of type *T*. Multiplication parameter *beta* for the sigmoid. If the input is not connected then the default value 1.0 is used. **Optional**
+
+**Outputs**:
+
+*   **1**: The resulting tensor of the same shape and type as input tensor.
+
+**Types**
+
+* *T*: arbitrary supported floating point type.
+
+
+**Example**
+
+```xml
+<layer ... type="Swish">
+    <input>
+        <port id="0">
+            <dim>256</dim>
+            <dim>56</dim>
+        </port>
+        <port id="1"/>
+    </input>
+    <output>
+        <port id="1">
+            <dim>256</dim>
+            <dim>56</dim>
+        </port>
+    </output>
+</layer>
+```

docs/ops/opset4.md

@@ -134,6 +134,7 @@ declared in `namespace opset4`.
 * [Squeeze](shape/Squeeze_1.md)
 * [StridedSlice](movement/StridedSlice_1.md)
 * [Subtract](arithmetic/Subtract_1.md)
+* [Swish](activation/Swish_4.md)
 * [Tan](arithmetic/Tan_1.md)
 * [Tanh](arithmetic/Tanh_1.md)
 * [TensorIterator](infrastructure/TensorIterator_1.md)