Add support for solc 0.5.0

* `py-solc` Version: 3.2.0
* `solc` Version: 0.5.0
* Python Version: 3.6.7
* OS: linux

To keep up to date with the latest changes, it would be nice to have support for the latest solc version. On my machine that'd be `0.5.0+commit.1d4f565a.Linux.g++` - installed from the Ethereum PPA:
`deb http://ppa.launchpad.net/ethereum/ethereum/ubuntu bionic main`

Background: [Mythril](https://github.com/ConsenSys/mythril-classic) is using py-solc as a wrapper to provide various solc versions as the contracts to scan require it. Having an up-to-date wrapper greatly helps us to keep our code clean from hacky workarounds. :slightly_smiling_face:

### What was wrong?
```
Traceback (most recent call last):
File "/home/spoons/diligence/mythril-classic/myth", line 9, in
mythril.interfaces.cli.main()
File "/home/spoons/diligence/mythril-classic/mythril/interfaces/cli.py", line 282, in main
enable_online_lookup=args.query_signature,
File "/home/spoons/diligence/mythril-classic/mythril/mythril.py", line 120, in __init__
self.solc_binary = self._init_solc_binary(solv)
File "/home/spoons/diligence/mythril-classic/mythril/mythril.py", line 245, in _init_solc_binary
solc.install_solc("v" + version)
File "/home/spoons/diligence/mythril-classic/.tox/py36/lib/python3.6/site-packages/solc/install.py", line 508, in install_solc
', '.join(sorted(INSTALL_FUNCTIONS[platform].keys())),
ValueError: Installation of solidity==v0.5.0 is not supported. Must be one of v0.4.1, v0.4.11, v0.4.12, v0.4.13, v0.4.14, v0.4.15, v0.4.16, v0.4.17, v0.4.18, v0.4.19, v0.4.2, v0.4.20, v0.4.21, v0.4.22, v0.4.23, v0.4.24, v0.4.25, v0.4.6, v0.4.7, v0.4.8, v0.4.9
```

#### Cute Animal Picture