title: Unable to use Robot Framework custom library which has written using Python
body: <p>Created a sample Python script( Elements.py) with a function like below:</p>
  
  <pre><code>from robot.api.deco import keyword
  
  @keyword("join two strings")
  def join_two_strings(arg1, arg2):
     return arg1 + " " + arg2
  </code></pre>
  
  <p>Then I have imported into Robot Framework script(.robot file) as a Library:</p>
  
  <pre><code>*** Settings ***
  Library                 AppiumLibrary
  Library                 Selenium2Library
  Library                 BuiltIn
  #Here is the import of Custom Lib
  Library                 Elements.py 
  
  *** Variable ***
  
  *** Test Cases ***
  Example that calls a Python keyword
     ${result}=   join two strings   hello world
     Should be equal     ${result}    hello world
  </code></pre>
  
  <p>After running above the script, getting error like "No keyword with name 'join two strings' found." even though where I have imported the Custom library.</p>
  
  <p>Error Message:</p>
  
  <pre><code>[ ERROR ] Error in file C:\Users\ramana.gouda\PycharmProjects\SafeMobile\Test_Suite\TestCase_346.robot: Test library 'Elements.py' does not exist.
  
  TestCase 346 :: Creating internal cases using device                          
  
  Example that calls a Python keyword                                   | FAIL |
  No keyword with name 'join two strings' found.
  </code></pre>