Statements-manager

- ADD (feature): Sample Input / Output Template 103
- The same as problemset template, you can edit the style of sample input / output text.
- ADD (feature): Support Cache 106
- When running `ss-manager run`, cache is also saved. It is used for checking whether there is no source file update or not.
- FIX: pdfkit version requirement 101
- FIX: comment to notice not to edit constraints file manually 102

Full changelog: https://github.com/tsutaj/statements-manager/compare/v1.6.1...v1.7.0

- FIX (bug): Markdown problemset output file
- The path to assets was incorrect (forgot path resolving)
- FIX: template files

- FIX: write `pragma once` in constraints file 87
- ADD (feature): generating problemset file (beta) 89
- assets are not supported (we want to support them at next release)

- FIX: rendering issue 84
- If proposed statements (e.g. addition, deletion, replacement) have remained, this application rendered all of them. This behavior is the cause of mixed version rendering, so we fixed this problem.
- FIX (minor issue): set default working directory 86
- set `.` (current directory) as default

- ADD (feature): ignore specified sample files 75
- You can use [Unix shell-style wildcards](https://docs.python.org/3/library/fnmatch.html).
- FIX: regard `*.diff` file as a sample output file 72
- FIX (bug): minor math-expression rendering issue 77
- FIX (bug): file naming rule 68