Unicodable should support ranges

So that this does not happen:

<liAealneDx> u: MINUS
<unicodable6> liAealneDx, U+002D HYPHEN-MINUS [Pd] (-)
<unicodable6> liAealneDx, U+00B1 PLUS-MINUS SIGN [Sm] (±)
<unicodable6> liAealneDx, 27 characters in total: https://gist.github.com/4a79f83a8d8b93dfc47d7b5de5dfd345
<liAealneDx> u: U+2212 U+2213 U+2214 U+2215
<unicodable6> liAealneDx, U+2213 MINUS-OR-PLUS SIGN [Sm] (∓)
<unicodable6> liAealneDx, U+2212 MINUS SIGN [Sm] (−)
<unicodable6> liAealneDx, 4 characters in total: https://gist.github.com/f580f51c9a402c88e08552d4ce6a77b3
<liAealneDx> u: U+2215 U+2216 U+2217 U+2218
<unicodable6> liAealneDx, U+2215 DIVISION SLASH [Sm] (∕)
<unicodable6> liAealneDx, U+2216 SET MINUS [Sm] (∖)
<unicodable6> liAealneDx, 4 characters in total: https://gist.github.com/49d402bde8d9fa97374cb41300bc998e
<liAealneDx> u: U+2218 U+2219 U+2220 U+2220 U+2221
<unicodable6> liAealneDx, U+2219 BULLET OPERATOR [Sm] (∙)
<unicodable6> liAealneDx, U+2218 RING OPERATOR [Sm] (∘)
<unicodable6> liAealneDx, 5 characters in total: https://gist.github.com/30558c21c0758ffeb88d4073087e1d45

You can already do it with a code block like this:

<liAealneDx> u: { 0x2100 < $_ < 0x2300 }
<unicodable6> liAealneDx, U+2101 ADDRESSED TO THE SUBJECT [So] (℁)
<unicodable6> liAealneDx, U+2102 DOUBLE-STRUCK CAPITAL C [Lu] (ℂ)
<unicodable6> liAealneDx, 511 characters in total: https://gist.github.com/1e39487db09287efbcb241d5630d3290

but a range syntax won't hurt, especially given that other bots support it for commits.

No files or tests are named. Start by locating the code that parses bot code blocks and handles the existing predicate range example, then compare its output with the listed Unicode results. Done means a range syntax is accepted and produces the expected character listing without changing existing code-block behavior.