Unicode Completion update

In IPython 7.1 the unicode completion map has been updated and synchronized with the Julia language.

Added and removed character characters:

\jmath (ȷ), \\underleftrightarrow (U+034D, combining) have been added, while \\textasciicaron have been removed

Some sequence have seen their prefix removed:

• 6 characters \text...<tab> should now be inputed with \...<tab> directly,
• 45 characters \Elz...<tab> should now be inputed with \...<tab> directly,
• 65 characters \B...<tab> should now be inputed with \...<tab> directly,
• 450 characters \m...<tab> should now be inputed with \...<tab> directly,

Some sequence have seen their prefix shortened:

• 5 characters \mitBbb...<tab> should now be inputed with \bbi...<tab> directly,
• 52 characters \mit...<tab> should now be inputed with \i...<tab> directly,
• 216 characters \mbfit...<tab> should now be inputed with \bi...<tab> directly,
• 222 characters \mbf...<tab> should now be inputed with \b...<tab> directly,

A couple of character had their sequence simplified:

• ð, type \dh<tab>, instead of \eth<tab>
• ħ, type \hbar<tab>, instead of \Elzxh<tab>
• ɸ, type \ltphi<tab>, instead of \textphi<tab>
• ϴ, type \varTheta<tab>, instead of \textTheta<tab>
• ℇ, type \eulermascheroni<tab>, instead of \Eulerconst<tab>
• ℎ, type \planck<tab>, instead of \Planckconst<tab>
• U+0336 (COMBINING LONG STROKE OVERLAY), type \strike<tab>, instead of \Elzbar<tab>.

A couple of sequences have been updated:

• \varepsilon now give ɛ (GREEK SMALL LETTER EPSILON) instead of ε (GREEK LUNATE EPSILON SYMBOL),
• \underbar now give U+0331 (COMBINING MACRON BELOW) instead of U+0332 (COMBINING LOW LINE).