Esparto

- New Features
- Links to Bootswatch CDN for page themes
- Reorganise and add options to `esparto.options`
- Table of Contents generator for Page element
- Save and Load config options
- Define Columns and Cards as dict of {"title": content}
- Add or replace Content by positional index
- New Layout Classes
- CardSection: Section with Cards as the default Content container
- CardRow: Row of Cards
- CardRowEqual: Row of equal width cards

- New Layout class
- Card: Bordered container for grouping content
- Updated Content class
- FigureMpl: SVG rendered plots now flex up to 150% of original size
- Other
- Defined string and repr representations for current settings
- Updated CSS to maintain distance from header if main title is not defined
- Updated content adaptor to allow other Layout objects as valid children for Column

* Implicitly read markdown text files

- New Layout classes
- Spacer: make an empty column within a Row
- PageBreak: enforce a page break in printed / PDF documents
- New Content class
- RawHTML: place raw HTML code in the page
- Updated Content classes
- DataFramePd: add new CSS style to minimise row height
- FigureMpl: SVG rendered plots are now responsive and horizontally centred
- New publishing features
- CSS stylesheet path can be passed to options.css_styles
- Jinja template path can be passed to options.jinja_template

- Update dependencies.
- Fix SVG rendering in PDF.
- Update docs and examples.

* Improve API.
* Responsive SVG plots.
* Update Jinja template to remove branding.
* Refactor codebase.