Fixed, tests for schema children protocol in src/{protocol,schema}.lisp

* src/protocol.lisp (schema-children): new generic function; return
  the items of a schema
  (find-child): new generic function; return a named child schema of a
  schema
  (setf find-child): new generic function; install a schema as a named
  child of another schema
  (find-child :around string t): new method; parse name strings
  (setf find-child :around t string t): likewise
  (find-child :around t t): new method; performs error signaling and
  error behavior
  (setf find-child :around t t t): likewise
* src/schema.lisp (schema::children): removed reader
  (schema-children standard-schema): new method; return child schemata
  of the schema
  (find-child t standard-schema): new method; return a child schema
  (setf find-child t sequence standard-schema): accept non-wild names;
  remove old child; cleaned up
  (setf find-child :after t t standard-schema): accept other keyword
  parameters
* src/package.lisp (package options): added exported symbols
  schema-children and find-child
* test/schema.lisp (test find-child.smoke): new test; smoke test for
  the `find-child' and (setf find-child) generic functions
Improved, added tests for commandline source in src/sources/source-commandline.lisp

* src/sources/source-cascade.lisp
  (shared-initialize :around common-cascade-source t): only add an
  entry for the commandline source if the :commandline provider of the
  "source" service can be found
* src/sources/source-commandline.lisp (commandline-source): renamed
  commandline -> commandline-source; added required slots; added
  documentation string
  (initialize commandline-source t): new method; store schema and
  create commandline options, synopsis and context keeping a mapping
  from commandline options to option names
  (make-option-using-type): new generic function; make a commandline
  option for a given option and type
  (define-make-option-using-type-method): new local macro; define some
  method on `make-option-using-type'
  (process commandline-source t): new method; retrieve values of
  commandline options created in `initialize'
* test/package.lisp (package options.test): added exported symbols
  make-random-string, mock-sink and sink-calls
  (make-random-string): moved here from test/sources/package.lisp;
  added case keyword parameter
  (notify mock-sink t t t): removed more "uninteresting" properties
* test/sources/source-cascade.lisp (test common-cascade-source.smoke):
  take into account the offset caused by the commandline option source
* test/sources/source-commandline.lisp: new file; contains test for
  commandline source
* test/sources/package.lisp (package options.sources.test): removed
  imported from options.test symbols mock-sink, sink-calls; added used
  package options.test
  (make-random-string): removed; moved to test/package.lisp
  (with-source-and-sink): added schema keyword parameter to allow
  calling `initialize' with a schema
* options.asd (system options-test): added file
  test/sources/source-commandline.lisp
Improvements, tests for ini syntax in src/sources/syntax-ini.lisp

* src/sources/syntax-ini.lisp
  (parser.ini:add-child ini-syntax list list): added continue restart;
  simplified
* test/sources/syntax-ini.lisp: new file; contains unit tests for ini
  syntax
* options-and-parser.ini.asd (header): fixed one-line summary and
  copyright
  (system options-and-parser.ini): fixed description;
  (system options-and-parser.ini-test): new system; tests for ini
  syntax
  (perform test-op eql options-and-parser.ini-test): new method; test
  options-and-parser.ini-test system
Added standard-synchronizer in src/synchronizer.lisp

* src/synchronizer.lisp: new file; contains synchronizer classes
* src/package.lisp (package options): added exported symbols
  synchronizer-target and standard-synchronizer
* test/synchronizer.lisp: new file; contains unit tests for
  synchronizer classes
* options.asd (system options): added file src/synchronizer.lisp
  (system options-test): added file test/synchronizer.lisp
Removed unused file src/sources/mixins.lisp

* src/sources/mixins.lisp: removed; was unused
* options.asd (system options): removed file src/sources/mixins.lisp