Removed use of FileType in argument specification

[toyg]

This allows us to handle files directly in lxml, which solves #72 and likely increases performance and exactness all around.

[regebro]

Looks good. I haven't thought about encodings with regards to patch files at all, but at least this should then not open them in cp1252 by default on Windows.

[coveralls]

Pull Request Test Coverage Report for Build 257

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 99.689%

---

Files with Coverage Reduction	New Missed Lines	%
xmldiff/main.py	1	98.8%

Totals
Change from base Build 255:	-0.1%
Covered Lines:	962
Relevant Lines:	965

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 257

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 99.689%

---

Files with Coverage Reduction	New Missed Lines	%
xmldiff/main.py	1	98.8%

Totals
Change from base Build 255:	-0.1%
Covered Lines:	962
Relevant Lines:	965

---

💛 - Coveralls

[regebro]

One unchanges line lost coverage? That must be a glitch. I think we can ignore that.