Merge pull request #371 from jbondpdx/puppet37

Puppet37
(DOC-1133) Mention file() function in module docs
DOC-1137: added always_cache_features to config_important_settings.markdown

Added to Puppet master settings, basics: the always_cache_features setting should be set to true to cache features whether or not the feature test succeeds.
DOC-1137 added link for always_cache_features

Added a link to configuration.html#always_cache_features:
DOC-1130 Added note re: deprecated node inheritance

Replaced most of the node inheritance information with a note that node inheritance is deprecated in Puppet 3.7.
DOCS-1148: resource collector can't collect classes

Added a note to lang_collectors.markdown that classes cannot be collected.