Resolve "libpbuild.bash: bugs in functions to compare versions"

Closes #130

See merge request !99

Resolve "modulecmd: use some defaults if Pmodules.conf does not exist"

Closes #129

See merge request !98

- if PMODULES_ENV is set but DefaultGroups, DefaultReleaseStages or
  ReleaseStages is not set in PMODULES_ENV, the the default defined in
  modulecmd is used

- defaults are set for DefaultsGroups, DefaultReleaseStages and ReleaseStages

Resolve "Sort versions numerically"

See merge request !97

- call sort with option --version-sort in getting available modules
  and search cmd

Resolve "terse output in sub-cmd avail is broken"

Closes #128

See merge request !96

Resolve "use term release stage in code, options and help"

Closes #127

See merge request !95

- refactor variables and function names
- internal: refactor UseFlags -> UsedFlags and change type to normal array

Resolve "rename variable DefaultUsedReleaseStages to DefaultReleaseStages"

Closes #125

See merge request !94

Resolve "review bash profile and init file"

Closes #124

See merge request !93

- introduce new configuration file ${PMODULES_ROOT}/config/Pmodules.conf
- move as much as possible from profile.bash and init/bash to
  modulecmd
- expose less environment variables to the user

Resolve "Refactor PMODULES_DEFAULT_GROUPS"

Closes #123

See merge request !92

Resolve "refactor PMODULE_DEFAULT_RELEASES"

Closes #122

See merge request !91

- new name is DefaultUsedReleaseStages

- new name is ReleaseStages

- new name is ReleaseStages

Resolve "modulecmd: switch sub-cmd need tmpfile"

Closes #120

See merge request !89

Resolve "modulecmd: fixes in loading a Pmodules module"

Closes #119

See merge request !88

Resolve "modulecmd: loading a Pmodules module"

Closes #118

See merge request !87

Merge branch '117-reinitialize-pmodules-environment-after-loading-a-new-pmodules-version' into 'master'

Resolve "reinitialize Pmodules environment after loading a new Pmodules version"

Closes #117

See merge request !86