- remove redundant concrete helper docs from declarative docs,
two places is enough

when cross-compiling from DDL to SQL, fixes #3615

- fix "version" got whacked into "f" in core tutorial
- fix short underline in automap
- fix unmatched boldface in session events

where the "default" argument was not included.
fixes #3605

for setting up baked lazy loaders would interfere with other
loader strategies that rely on lazy loading as a fallback, e.g.
joined and subquery eager loaders, leading to ``IndexError``
exceptions at mapper configuration time.
fixes #3612

to the :class:`.mutable.MutableDict` class.
fixes #3605

directly or within lazy loads, didn't consider the mapper's "get clause"
as part of the cache key, causing bound parameter mismatches if the
clause got re-generated.  This clause is cached by mappers
on the fly but in highly concurrent scenarios may be generated more
than once when first accessed.
fixes #3597