Merge remote-tracking branch 'shell/namespaced' into namespaced

This is a no-op merge, explicitly considering and rejecting the
tool-level removal of the hello script.  This avoids merge conflicts
if an aggregation branch wants to merge both our namespaced branch and
the tool-level namespaced branch.

* shell/namespaced: (91 commits)
  modular/shell: Start reorganizing the shell material
  Changing 'git clone' URL in shell README to the read-only git:// URL.
  Fix shell header
  Added some words about the history command and bang-history # direct access.
  Fix old typo on file size.
  Clean up ambiguity between file and filename.
  There is no executable in the boot-camps directory - need to cd to shell dir first.
  remove some spaces getting in the way of bold
  Seem to have the tables figured out - they need a header - annoying
  Can we get some documentation on tables
  A few more changes to be consistent and clear.
  Some formatting and flow changes:
  Update shell/Readme.md
  Update shell/Readme.md
  Update shell/Readme.md
  shell/Readme.md: Fix 'swsc' -> 'swc' typo
  shell/Readme.md: Use USERNAME and YYYY-MM-PLACE in git clone instructions
  fixed links
  shell/Readme.md: use explicit URL (with https://)
  Conversion of all rst to corresponding markdown files
  ...