v0.4.0

MatrixMarket v0.4.0

Diff since v0.3.1

Closed issues:

• Cannot open .mtx files from Network Data Repository (networkrepository.com). Not a valid header (#37)
• Read of skew-symmetric matrix only shows lower triangle (#39)

Merged pull requests:

• More detailed error message for header parse failure (#38) (@tkonolige)
• Change -11 -> -1 in skew symmetric. (#40) (@tkonolige)
• Add mmwrite to README (#41) (@jkrch)
• Modernize package and update CI (#43) (@amontoison)
• Update CI scripts (#45) (@amontoison)
• Bump version to v0.4.0 (#49) (@tkonolige)