Document template parameters in /prim

[mcol]

Summary

This adds and improves documentation of template parameters in /prim and fixes a few typos here and there. Closes #1473.

Tests

This is only documentation.

Side Effects

None.

Checklist

• Math issue consistent documentation of row/col template parameters to Eigen::Matrix #1473

• Copyright holder: Marco Colombo

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • docs build, (make doxygen)

[bob-carpenter]

Wow! This is a heroic amount of copy editing, and not just simple spell checking. Thanks so much.

[bob-carpenter]

This is good to merge when tests pass.

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	4.86	4.97	0.98	-2.33% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.99	-1.49% slower
eight_schools/eight_schools.stan	0.09	0.09	0.99	-0.86% slower
gp_regr/gp_regr.stan	0.22	0.22	1.0	-0.41% slower
irt_2pl/irt_2pl.stan	6.06	6.07	1.0	-0.2% slower
performance.compilation	89.4	87.5	1.02	2.13% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	7.31	7.3	1.0	0.08% faster
pkpd/one_comp_mm_elim_abs.stan	21.4	20.95	1.02	2.1% faster
sir/sir.stan	91.91	92.41	0.99	-0.54% slower
gp_regr/gen_gp_data.stan	0.04	0.05	0.95	-4.75% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.99	2.99	1.0	0.02% faster
pkpd/sim_one_comp_mm_elim_abs.stan	0.3	0.32	0.95	-5.67% slower
arK/arK.stan	1.76	1.75	1.01	0.61% faster
arma/arma.stan	0.76	0.79	0.96	-4.11% slower
garch/garch.stan	0.63	0.63	1.01	0.82% faster
Mean result: 0.990851998625

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Jenkins Console Log
Blue Ocean
Commit hash: e63f802

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Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix