New data-rearrangers: nest, shuffle, repeat; misc. features

Major features in this release:

• mlr nest is a companion to mlr reshape which was introduced in Miller 3.4.0: it allows unpacking key-value pairs which are nested within field values, and repacking them. Please see http://johnkerl.org/miller/doc/reference.html#nest.
• mlr shuffle is a simple output-record permutor: http://johnkerl.org/miller/doc/reference.html#shuffle
• mlr repeat can be used as a data-generator, to expand a few input records (or even a single one) into arbitrarily many. This is particularly useful in conjunction with pseudorandom-number generators. As well, it can be used to reconstruct individual samples from data which have been count-aggregated, so that statistics such as mode, percentiles, etc. may be computed on them. Please see http://johnkerl.org/miller/doc/reference.html#repeat.
• mlr put and mlr filter now accept a -f {filename} option, so that the DSL expression may be placed within a file instead of being typed out on the command line when desired. Please see http://johnkerl.org/miller/doc/reference.html#put and http://johnkerl.org/miller/doc/reference.html#filter.

Minor features:

• put/filter DSL string literals now may include \t, \", etc.: e.g. mlr put '$out = $left . "\t" . $right'
• There is now a typeof function for the put/filter DSLs: mlr put '$xtype = typeof($x)'. This is occasionally useful for debugging type-conversion questions.
• You may now do mlr --nr-progress-mod 1000000 ... to get something printed to stderr every 1000000th input record, and so on. For long-running aggregations on large input file(s), this can provide reassurance that processing is indeed proceeding apace. Example:

$ mlr --nr-progress-mod 100000 check data/big.dkvp
NR=100000 FNR=100000 FILENAME=data/big.dkvp
NR=200000 FNR=200000 FILENAME=data/big.dkvp
NR=300000 FNR=300000 FILENAME=data/big.dkvp
NR=400000 FNR=400000 FILENAME=data/big.dkvp
NR=500000 FNR=500000 FILENAME=data/big.dkvp
NR=600000 FNR=600000 FILENAME=data/big.dkvp
NR=700000 FNR=700000 FILENAME=data/big.dkvp
...

• mlr cat -n had a bug wherein it counted zero-up while its documentation claimed it counted one-up. Now it counts one-up as documented.