New, documented pylint configuration

The pylint configuration in .pylint was a modified version of the
output of `pylint --generate-rcfile` from an unknown version of
pylint. Replace it with a file that only contains settings that are
modified from the default, with an explanation of why each setting is
modified.

The new .pylintrc was written from scratch, based on the output of
pylint on the current version of the files and on a judgement of what
to silence generically, what to silence on a case-by-case basis and
what to fix.

.pylintrc

@@ -0,0 +1,52 @@
+[BASIC]
+# We're ok with short funtion argument names.
+# [invalid-name]
+argument-rgx=[a-z_][a-z0-9_]*$
+
+# Allow filter and map.
+# [bad-builtin]
+bad-functions=input
+
+# We prefer docstrings, but we don't require them on all functions.
+# Require them only on long functions (for some value of long).
+# [missing-docstring]
+docstring-min-length=10
+
+# Allow longer methods than the default.
+# [invalid-name]
+method-rgx=[a-z_][a-z0-9_]{2,35}$
+
+# Allow module names containing a dash (but no underscore or uppercase letter).
+# They are whole programs, not meant to be included by another module.
+# [invalid-name]
+module-rgx=(([a-z_][a-z0-9_]*)|([A-Z][a-zA-Z0-9]+)|[a-z][-0-9a-z]+)$
+
+# Some functions don't need docstrings.
+# [missing-docstring]
+no-docstring-rgx=(run_)main$
+
+# We're ok with short local or global variable names.
+# [invalid-name]
+variable-rgx=[a-z_][a-z0-9_]*$
+
+[DESIGN]
+# Allow more than the default 7 attributes.
+# [too-many-instance-attributes]
+max-attributes=15
+
+[FORMAT]
+# Allow longer modules than the default recommended maximum.
+# [too-many-lines]
+max-module-lines=2000
+
+[MESSAGES CONTROL]
+disable=
+
+[REPORTS]
+# Don't diplay statistics. Just the facts.
+reports=no
+
+[VARIABLES]
+# Allow unused variables if their name starts with an underscore.
+# [unused-argument]
+dummy-variables-rgx=_.*