Reorganize paperspec commands and pin dependency versions (#2)

Reviewed-on: #2

docs/walkthrough.md

@@ -13,7 +13,7 @@ It has nothing to do with the repository's name.
 
 Open [fixtures/packages/hale2026harmonic-damb/](../fixtures/packages/hale2026harmonic-damb/) beside this page, because every ID below is in it.
 A package is a folder of files, mostly JSON Lines (`.jsonl`: one JSON record per line).
-The hand-written source of the first reading is [fixtures/src/hale2026harmonic.json](../fixtures/src/hale2026harmonic.json); no converter ran on it, and [`tools/build.py`](../tools/build.py) expands it into the package.
+The hand-written source of the first reading is [fixtures/src/hale2026harmonic.json](../fixtures/src/hale2026harmonic.json); no converter ran on it, and [`paperspec build`](../src/paperspec/cli/build.py) expands it into the package.
 Each step says what a converter, a person or a checker does.
 
 ## 1. A PDF arrives
@@ -166,7 +166,7 @@ It is a [Frictionless Data Package](https://datapackage.org/standard/data-packag
 Its CSV keeps every digit as printed (`1.526` and `1.5260` stay different), and every value has an anchor to the cell that prints it, so a claim that rests on a value can show the cell.
 The descriptor types the fields as numbers; how a generic Data Package tool treats `1.5260` was not verified.
 All twelve value anchors resolve as `current`.
-The reference checker, [`tools/check.py`](../tools/check.py), confirms each CSV value equals its cell's text.
+The reference checker, [`paperspec check`](../src/paperspec/cli/check.py), confirms each CSV value equals its cell's text.
 
 ## 8. Sharing without the text