Allow customizable modbus timeout

[samc1213]

Description

Allow customization of the Modbus timeout

Issues Resolved

Check List

General

• [ x] Code follows coding style defined in STYLE.md
• [ x] Doxygen comments are included inline with code
• [ x] No unnecessary whitespace; check with git diff --check before committing.

The following have been modified to reflect new features, if warranted

• [ x] README.md
• [ ] keywords.txt (use tabs as whitespace separators)
• [ ] library.properties
• [ ] examples/ - update or create new ones, as warranted

The following have NOT been modified

• [ x] doc/ - will be updated upon versioned release
• [x ] .ruby-gemset
• [ x] .ruby-version
• [ x] CHANGELOG.md - will be updated upon versioned release (HISTORY.md is deprecated)
• [ x] Gemfile
• [ x] LICENSE
• [ x] VERSION - will be updated upon versioned release