text: Title: Connection string does not parse hash character properly
  Body: * **asyncpg version**: 0.18.3
  * **PostgreSQL version**: 11.5
  * **Do you use a PostgreSQL SaaS?  If so, which?  Can you reproduce
    the issue with a local PostgreSQL install?**: Reproduced locally
  * **Python version**: 3.7.4
  * **Platform**: macOS, Debian
  * **Do you use pgbouncer?**: No
  * **Did you install asyncpg with pip?**: Yes
  * **If you built asyncpg locally, which version of Cython did you use?**: N/A
  * **Can the issue be reproduced under both asyncio and
    [uvloop](https://github.com/magicstack/uvloop)?**: Didn't try yet
  
  Similar issue to #429 . If the password includes a `#` character, you get the following error:
  `ValueError: invalid literal for int() with base 10:`
  
  The URI I was using looked like: `postgresql://postgres:abcd&#12@127.0.0.1:5432/db`, and `psql` parses it correctly.
  
  When you remove the `#`, it works fine.