Client support for compressed transfer encoding

## Long story short
aiohttp does not support any transfer encoding other than chunking. Responses from servers using e.g. `Transfer-Encoding: gzip` result in the compressed payload. Worse yet, those applying both compression and chunking result in the raw payload with chunking still intact (but only when using the C parser!).

## Expected behaviour
Decompressed payload.

## Actual behaviour
Compressed or compressed + chunked payload.

## Steps to reproduce
A simple server and client illustrating this issue can be found in [this gist](https://gist.github.com/JustAnotherArchivist/ba23cb434810254a7d55ec893e45e1d4). I wrote a single test client and server for both this issue and #4436; the first line is irrelevant to this issue and not included in the output below.

Expected output:
```
> python3 client.py | tail -n+2
b'Test'
b'Test'
```

Actual output:
```
> python3 client.py | tail -n+2
b'\x1f\x8b\x08\x00\x82Y\xf0]\x02\xff\x0bI-.\x01\x002\xd1Mx\x04\x00\x00\x00'
b'5\r\n\x1f\x8b\x08\x00\x82\r\n13\r\nY\xf0]\x02\xff\x0bI-.\x01\x002\xd1Mx\x04\x00\x00\x00\r\n0\r\n\r\n'
```

However, when running it with the pure-Python parser, the chunked TE gets handled in the second case, and the output is:
```
> AIOHTTP_NO_EXTENSIONS=1 python3 client.py | tail -n+2
b'\x1f\x8b\x08\x00|\\\xf0]\x02\xff\x0bI-.\x01\x002\xd1Mx\x04\x00\x00\x00'
b'\x1f\x8b\x08\x00|\\\xf0]\x02\xff\x0bI-.\x01\x002\xd1Mx\x04\x00\x00\x00'
```

## Your environment
I tested this with aiohttp 2.3.10 and Python 3.6.9 on Debian, but based on the current aiohttp code, the behaviour should still be the same on the current versions.