dzil: keep Pod::Weaver from changing code line numbers

This will keep any errors reporting from end-users nearly matching the
corresponding line numbers in the source.

When version number munging doesn't add a line, then the released code
lines and repo code lines will match.

Lines numbers of POD after the __END__ will change, but that won't
affect error messages.
dzil: set is_trial in dist.ini
dzil: keep $VERSION in files in repo

This commit adds a $VERSION declaration to all *.pm files.  The version
now uses the more standard "leading-v" form: vX.Y.Z.

The dist.ini is updated to do the following:

* sets "is_trial" to true to force -TRIAL versions until we're ready for
  a stable release

* sets distribution version to that found in lib/MongoDB.pm

* rewrites $VERSION in built distribution files for any version override
  or with a comment to indicate trial release status

* adds an xt test to confirm that versions exist in every module

* adds a plugin to bump versions in source files after release

* splits post-release commit into two phases: one before munging
  and one after

* automatically tags Changes with version and timestamp on release

* other minor changes to account for the above changes
Changes: stub a section for next release
dzil: reorganize and annotate dist.ini
dzil: gather only git-tracked files
dzil: add generated test to show prerequisite versions
dzil: add extra t/ and xt/ tests and get code passing them
ignore config.log from Config::AutoConf
dzil: add more pre-release checks and reorder
dzil: use custom PAUSE identity file for uploading
dzil: remove rendundant Repository plugin

The GithubMeta plugin already sets repo metadata correctly.
dzil: revise generation of no_index metadata

Changed to use the core Dist::Zilla plugin.  Removed the legacy 'ext'
directory and added 'xt'.
dzil: add comments to plugins without them
dzil: generate 'provides' metadata
dzil: move RunExtraTests later in dist.ini to avoid rebuilds during dzil test --all
dzil: s/Config::Auto/Config::AutoConf/