eval,parser: implement binary-| eval

[sbinet]

Fixes neugram/ng#196.

[codecov-io]

Codecov Report

Merging #202 into master will decrease coverage by 0.46%. The diff coverage is 7.69%.

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   50.79%   50.33%   -0.47%     
==========================================
  Files          22       22              
  Lines       10174    10252      +78     
==========================================
- Hits         5168     5160       -8     
- Misses       4504     4588      +84     
- Partials      502      504       +2

Impacted Files	Coverage Δ
format/expr.go	48.16% <0%> (-4.45%)	:arrow_down:
format/tipe.go	69.59% <0%> (-1.72%)	:arrow_down:
eval/op.go	30.22% <11.53%> (-1.38%)	:arrow_down:
parser/scanner.go	66.93% <0%> (-2.2%)	:arrow_down:
parser/parser.go	70.05% <0%> (-0.22%)	:arrow_down:

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[sbinet]

I've rebased this PR on top of #213 (so as to not disable then re-enable the TableLiteral typecheck test.) PTAL.

[crawshaw]

LGTM