BibConvert: lxml support for local document()

* Adds support for document() usage in XSLT stylesheets for
  the lxml processor.

* Removes Exception masking.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>

Will make a separate PR for `next`.
4: I102 copyright year is outdated, expected 2014 but got 2012
49:6: E126 continuation line over-indented for hanging indent
94:60: E502 the backslash is redundant between brackets
99:1: E302 expected 2 blank lines, found 1
99: D400 First line should end with '.', not ':'
99: D205 Blank line missing between one-line summary and description
132:76: E502 the backslash is redundant between brackets
133:37: E502 the backslash is redundant between brackets
138:1: E302 expected 2 blank lines, found 1
138: D200 One-line docstring should not occupy 3 lines
161:76: E502 the backslash is redundant between brackets
162:37: E502 the backslash is redundant between brackets
167:1: E302 expected 2 blank lines, found 1
167: D400 First line should end with '.', not ':'
167: D205 Blank line missing between one-line summary and description
192:76: E502 the backslash is redundant between brackets
193:37: E502 the backslash is redundant between brackets
198:1: E302 expected 2 blank lines, found 1
198: D200 One-line docstring should not occupy 3 lines
213:76: E502 the backslash is redundant between brackets
214:37: E502 the backslash is redundant between brackets
219:1: E302 expected 2 blank lines, found 1
219: D400 First line should end with '.', not ':'
219: D205 Blank line missing between one-line summary and description
244:76: E502 the backslash is redundant between brackets
245:37: E502 the backslash is redundant between brackets
250:1: E302 expected 2 blank lines, found 1
250: D200 One-line docstring should not occupy 3 lines
258:1: E302 expected 2 blank lines, found 1
258: D401 First line should be imperative: 'Processe', not 'Processes'
293:53: E225 missing whitespace around operator
296:49: E225 missing whitespace around operator
299:45: E225 missing whitespace around operator
368:66: E502 the backslash is redundant between brackets
375:64: E502 the backslash is redundant between brackets
399:43: E128 continuation line under-indented for visual indent
400:43: E128 continuation line under-indented for visual indent