Builders

[DavisVaughan]

• ones() just use rray()
• zeros() just use rray()
• ones_like()
• zeros_like()
• eye() (blocked by Is eye() specific to row major layouts? xtensor-stack/xtensor-r#90)
• arange() just use 1:10 or seq() for equal spacing
• linspace() use seq()
• logspace() not that useful
• concatenate() (this could be useful) (probably impossible with their tuple impl, use rray_bind())
• stack() maybe (probably impossible with their tuple impl, use rray_bind())
• diag() but probably a different name
• diagonal() (blocked by Let xt::diagonal() return results in a column major fashion xtensor-stack/xtensor#1570)
• tril() but call it tri_lower() (likely also blocked by 1570)
• triu() but tri_upper() (likely also blocked by 1570)