Implement GetElementTextHandler.
Add getting text from text fields.
For more efficient to get the control pattern, change to use TryGetCurrentPattern instead of GetCurrentPropertyValue.
Merge branch 'master' into implement_get_text_handler

Conflicts:
	src/WinAppDriver/Program.cs
	src/WinAppDriver/WinAppDriver.csproj
Ignore .suo (Solution User Options) files.
Merge pull request #3 from imsardine/implement_get_text_handler

Implement GetElementTextHandler.