Initial Java 8 support

[dbaxa]

adds support for lambda expressions and method/constructor references.

[dbaxa]

cc @c2nes

[c2nes]

Looks like this is unused and could be removed.

[dbaxa]

@c2nes can we merge this code with the MethodReference limitations (see #18 (comment)) ?

[c2nes]

Sorry for the long delay @dbaxa. Thank you very much for the contribution!

[dbaxa]

Thank you for merging this :-)

[manoelcampos]

The javalang 0.10.1 parses default and static interface's methods of Java 8 but there is some issue with the version available via pip. Using pip 9.0.1 it downloads javalang 0.10.1 as shown below:

pip show javalang 
Name: javalang
Version: 0.10.1

However, it is raising exceptions when an interface has default or static methods.
The version installed by pip is different from the one available at GitHub, as the diff from file parser.py shows:

1051a1052
>         body = None
1056c1057,1060
<         self.accept(';')
---
>         if self.would_accept('{'):
>             body = self.parse_block()
>         else:
>             self.accept(';')
1059a1064
>                                       body=body,
1065a1071
>         body = None
1070c1076,1079
<         self.accept(';')
---
>         if self.would_accept('{'):
>             body = self.parse_block()
>         else:
>             self.accept(';')
1073c1082,1083
<                                       throws=throws)
---
>                                       throws=throws,
>                                       body=body)

[dbaxa]

cc @c2nes