add substitutions for selected text

[anb0s]

Substitutions for text selected in editor should be proveded:

• selected text start line (same as resource_line_number in add substitution variable for line_number #212 )
• selected text end line
• selected text length
• selected text offset
• selected text

[anb0s]

see PR #220

[anb0s]

• ${easyshell:resource_line_number} = line number (within view or editor)
• ${easyshell:selected_text_start_line} = selected text start line (within view or editor), it's equal to ${easyshell:resource_line_number}
• ${easyshell:selected_text_end_line} = selected text end line (within view or editor)
• ${easyshell:selected_text_length} = selected text length (within view or editor)
• ${easyshell:selected_text_offset} = selected text offset (within view or editor)
• ${easyshell:selected_text} = selected text (within view or editor)

[anb0s]

see new pre-release v2.3.0-beta.2
that also includes chnages from pre-release v2.3.0-beta.1