Fix various grammar/style/type issues in 0.4.2.1-alpha changelog

  o Minor features (best practices tracker):

    - Our best-practices tracker now integrates with our include-checker

      tool to keep track of how many layering violations that we have

      not yet fixed. We hope to reduce this number over time to improve

      Tor's modularity. Closes ticket 31176.

      tool to keep track of how many layering violations we have not yet

      fixed. We hope to reduce this number over time to improve Tor's

      modularity. Closes ticket 31176.

    - Add a TOR_PRACTRACKER_OPTIONS variable for passing arguments to

      practracker from the environment. We may want this for continuous

      integration. Closes ticket 31309.

    - Give a warning rather than an error when a practracker exception

      is violated by a small amount; add a --list-overbroad option to

      is violated by a small amount, add a --list-overbroad option to

      practracker that lists exceptions that are stricter than they need

      to be, and provide an environment variable for disabling

      practracker. Closes ticket 30752.

      routerinfos, routerstatuses, and nodes. Closes ticket 21003.

  o Minor features (onion service v3):

    - Do not allow single hop client to fetch or post an HS descriptor

    - Do not allow single hop clients to fetch or post an HS descriptor

      from an HSDir. Closes ticket 24964.

  o Minor features (onion service):

    - Disallow single-hop clients at the introduction point. We've

      removed Tor2web support a while back and single-hop rendezvous

      ttempts are blocked at the relays. This change should remove load

      attempts are blocked at the relays. This change should remove load

      off the network from spammy clients. Close ticket 24963.

  o Minor features (stem tests):

      31657; bugfix on 0.3.3.1-alpha.

  o Minor bugfixes (ipv6):

    - We check for private IPv6 address alongside their IPv4 equivalents

    - Check for private IPv6 addresses alongside their IPv4 equivalents

      when authorities check descriptors. Previously, we only checked

      for private IPv4 addresses. Fixes bug 31088; bugfix on

      0.2.3.21-rc. Patch by Neel Chauhan.

  o Minor bugfixes (onion service v3):

    - When purging the client descriptor cache, close any introduction

      point circuits associated with purged cache entries. This avoids

      picking those circuits later when connecting to them later. Fixes

      bug 30921; bugfix on 0.3.2.1-alpha.

      picking those circuits later when connecting to the same

      introduction points. Fixes bug 30921; bugfix on 0.3.2.1-alpha.

  o Minor bugfixes (onion services):

    - In the hs_ident_circuit_t data structure, remove the unused field

      more general tool. Now typed structure members are accessible via

      an abstract type. Implements ticket 30914.

    - Move our backend logic for working with configuration and state

      files into a lower-level library, since in no longer depends on

      files into a lower-level library, since it no longer depends on

      any tor-specific functionality. Closes ticket 31626.

    - Numerous simplifications in configuration-handling logic: remove

      duplicated macro definitions, replace magical names with flags,