Release 0.2.12

[cuviper]

bors r+

[bors[bot]]

Build succeeded:

• Test (1.26.0)
• Test (1.15.0)
• Test (stable)
• Test (1.20.0)
• Format
• Test (i586)
• No Std
• Test (nightly)
• Test (1.8.0)
• Test (1.31.0)
• Test (beta)