Fix and format code example in README
Fix errors and warnings pointed out by Eclipse PyDev code analysis

Mostly unused imports and variables, non-standard indentation.
Some real errors.
Should be clear what the problem was from the diff.
Conflicts:

	astroquery/tests/test_besancon.py
	astroquery/tests/test_irsa.py

(resolved: there were just excess imports, afaik)
fixed SIMBAD examples per cdeil's findings
overwrite=True in magpis tests to avoid boring "file already exists"
error
added code-block markup