decorators use now functools.wraps - close #9
new module testlinkargs and factory decoMakerApiCallWithArgs() #8

module testlinkargs is used as a 'singleton' to register the supported
TestLink API methods and there (positional and optional) arguments
- replace testlinkapigeneric.positionalArgNamesDefault

new decorator factory decoMakerApiCallWithArgs() 
- realize, that the decorator decoApiCallWithArgs could register API
methods and there arguments with new function
testlinkargs.registerMethod()
decorator decoApiCallAddDevKey registers argument 'devKey' #8
decorators separated into module testlinkdecorators #8

separation makes module testlinkapigeneric more readable
whatArgs(apiMethodName) implemented #8
cleanup of api method doc strings, closes #8

example about description of all implemented api method 

```
import testlink
tlh = testlink.TestLinkHelper()
tls = tlh.connect(testlink.TestlinkAPIGeneric)
for m in testlink.testlinkargs._apiMethodsArgs.keys():
    print tls.whatArgs(m), '\n'

```