Please handle this together with sr#1157907, this needs the updated libxpp
version.

- Update to version 1.0+git3df8353:
* README.md: document configuration file support
* nst: make external command to receive terminal buffer configurable
* doc: update and complement man pages
* nst: support extra configuration file specified in environment variable
* Cmdline: support additional config file specification
* SConstruct files: fix flake8 findings
* XEventHandler: support ConfigFile override of KbdShortcuts
* themes: gruvbox: fix invalid reverse cursor color index
* nst: support color configuration via ConfigFile
* Screen: asText(): don't add newlines for wrapped lines
* themes: make theme configurable via ConfigFile
* global: use runtime defined Theme structure
* Theme: use std::vector for extended colors
* Selection: make SEL_URI_SCHEMES configurable via ConfigFile
* Term: make HISTORY_LEN configurable via ConfigFile
* WindowSystem: make HIDE_MOUSE_CURSOR configurable via ConfigFile
* Term: make KEEP_SCROLL_POSITION configurable via ConfigFile
* WindowSystem: support configuration of COLS and ROWS via ConfigFile
* WindowSystem: support configuration of CURSORSHAPE via ConfigFile
* WindowSystem: make CURSOR_THICKNESS configurable via ConfigFile
* nst: make BLINK_TIMEOUT configurable via ConfigFile
* Selection: make SEL_LINE_SNAP_KEEP_NEWLINE configurable via ConfigFile
* XEventHandler: support configuring SEL_CLEAR via ConfigFile
* ConfigFile: support obtaining boolean config values
* WindowSystem: support configuration of BORDER_PX via ConfigFile
* TTY: bad SIGCHILD handling logic
* Selection: support configuring WORD_DELIMITERS via configuration file
* ConfigFile: support getting wstring config values
* ConfigFile: support unicode strings and proper string quoting style