emacs: Rewrite scheme side in a functional manner.

emacs: Rewrite scheme side in a functional manner.

* emacs/guix-main.scm: Rewrite in a functional way.  Add support for output
  entries.
  (%current-manifest, %current-manifest-entries-table,
  set-current-manifest-maybe!): Replace with...
  (manifest-entries->hash-table, manifest->hash-table): ... this.
  (manifest-entries-by-name+version): Replace with...
  (manifest-entries-by-name): ... this.
  (fold-manifest-entries): Rename to...
  (fold-manifest-by-name): ... this.
  (package-installed-param-alist): Rename to...
  (%manifest-entry-param-alist): ... this.
  (package-param-alist): Rename to...
  (%package-param-alist): this.
  (manifest-entry->installed-entry): Rename to...
  (manifest-entry->sexp): ... this.
  (manifest-entries->installed-entries): Rename to...
  (manifest-entries->sexps): ... this.
  (matching-generation-entries): Replace with...
  (matching-generations): ... this.
  (last-generation-entries): Replace with...
  (last-generations): ... this.
  (get-entries): Rename to...
  (entries): ... this.
  (installed-entries-by-name+version, installed-entries-by-package,
  matching-package-entries, fold-object, package-entries-by-name+version,
  package-entries-by-spec, package-entries-by-regexp, package-entries-by-ids,
  newest-available-package-entries, all-available-package-entries,
  manifest-package-entries, installed-package-entries,
  generation-package-entries, obsolete-package-entries,
  all-generation-entries, generation-entries-by-ids, profile-generations,
  %package-entries-functions, %generation-entries-functions): Remove.
  (manifest=?, manifest-entry->name+version+output, manifest-entry-by-output,
  list-maybe, matching-packages, filter-packages-by-output, packages-by-name,
  manifest-entry->packages, all-available-packages, newest-available-packages,
  specification->package-pattern, specification->output-pattern,
  id->package-pattern, id->output-pattern, specifications->package-patterns,
  specifications->output-patterns, ids->package-patterns,
  ids->output-patterns, manifest-patterns-result, obsolete-package-patterns,
  obsolete-output-patterns, manifest-package-patterns,
  manifest-output-patterns, obsolete-package-sexp,
  package-pattern-transformer, output-pattern-transformer, entry-type-error,
  search-type-error, pattern-transformer, patterns-maker,
  package/output-sexps, find-generations, generation-sexps): New procedures.
  (%pattern-transformers, %patterns-makers): New variables.
* emacs/guix-base.el (guix-continue-package-operation-p): Adjust accordingly.
* emacs/guix-info.el (guix-package-info-insert-action-button): Likewise.