added gmail steps (#49)

Author: AlexGalichenko

docs/Steps/gmail.md

@@ -0,0 +1,77 @@
+---
+sidebar_position: 8
+---
+
+# @qavajs/steps-gmail
+Step library to test emails via gmail client
+
+## Installation
+`npm install @qavajs/steps-gmail`
+
+## Configuration
+```javascript
+module.exports = {
+    default: {
+        require: ['node_modules/@qavajs/steps-gmail/index.js'],
+        gmail: {
+            timeout: 30000, // timeout to wait email delivery
+            interval: 5000 // interval to check email delivery
+        }
+    }
+}
+```
+
+## Email Steps
+--------------
+### I log in to gmail as {string}
+
+Login to gmail
+
+|     param      |  type  |                             description                              | 
+|:--------------:|:------:|:--------------------------------------------------------------------:|
+| credentialsKey | string | memory key that resolves to Gmail auth object (google.auth.fromJSON) |
+
+credentials key should resolve to object like:
+```json
+{
+    "type": "authorized_user",
+    "client_id": "client_id",
+    "client_secret": "client_secret",
+    "refresh_token": "refresh_token"
+}
+```
+example:
+```gherkin
+When I log in to gmail as '$gmailUser'
+```
+                     
+--------------
+### I wait email matching {string}
+
+Wait until email matching advanced search syntax query to exist
+
+|    param    |  type  |                               description                                | 
+|:-----------:|:------:|:------------------------------------------------------------------------:|
+| searchQuery | string | advanced search syntax query https://support.google.com/mail/answer/7190 |
+
+example:
+```gherkin
+When I wait email matching 'subject:some subject'
+```
+
+--------------
+### I save email matching {string} as {string}
+
+Save email matching advanced search syntax query to memory as https://nodemailer.com/extras/mailparser/ object
+If query returns multiple message only first one will be saved.
+
+|    param    |  type  |                               description                                | 
+|:-----------:|:------:|:------------------------------------------------------------------------:|
+| searchQuery | string | advanced search syntax query https://support.google.com/mail/answer/7190 |
+|  memoryKey  | string |                         memory key to save email                         |
+
+example:
+```gherkin
+When I save email matching 'subject:some subject' as 'email'
+Then I expect '$email.subject' to equal 'some subject'
+```