Signxml

- Update dependencies to baseline on Ubuntu 18.04

- Clarify documentation of Ubuntu installation dependencies

- List ipaddress as a dependency

- Strip PEM header from OpenSSL.crypto.X509 cert

- Doc updates: dependency versions, standard links

- Fix cryptography deprecation warnings. Closes 108

- Allow URI attribute of Reference to be absent (102)

- Fix release

Fix release

- Relax dependency version constraints.

- Drop Python 3.3 support.

- Support for PEM files with CR+LF line endings (93).

- Import asn1crypto on demand

- Allow newer versions of cryptography library (89)

- Add explicit dependency on asn1crypto to setup.py (87)

- Remove use of Exception.message for py3 compatibility. Closes 36 (86)

- Use asn1crypto instead of pyasn1 to match cryptography lib (85)

- Pin to major version of lxml instead of minor

- Allow newer versions of several requirements (84)

- Allow newer version of eight library (83)