glue.ligolw.ligolw:  introduce attributeproxy mechanism

- and add proxies for all element attributes except Param's
glue.ligolw.param:  fix some namespace bugs
glue.ligolw.param:  port to attributeproxy mechanism

- also,  don't put newlines around content
- and use super() to chain to parent's .__init__()
glue.ligolw.array:  port to attributeproxy mechanism
glue.ligolw.table:  port to attributeproxy mechanism
glue/test:

- in ligo_lw_test_01 add Param tests
- also try writing the document to /dev/null to see if the document
  triggers writing errors
- aesthetic tweaks of web server macros
- and add a final "all tests passed" message
- expand unit tests to exercise array.from_array()
port some glue.ligolw pylal code to attributeproxy mechanism
glue.ligolw.ligolw:  simplify some loops in Element

- fixes failure of .removeChild() to raise ValueError if the requested
  element is not a child of self
dagfile:  edit documentation
glue.dagfile:  simplify an enumerate()