Various search related improvements, smartparens, web-mode and golden-ratio tweaks

• new documentation section: Seaching (https://github.com/syl20bnr/spacemacs#searching)
• the behavior of * has been improved, in visual state, * performs a search of the selected region using evil-visualstar. In the other states, * performs a search of the symbol/word under point using auto-highlight-symbol
• auto-highlight-symbol now highlights any symbol in comments and strings
• key to change the range of auto-highlight-symbol is now r instead of c
• evil-search-highlight-persist has been added, to clear the highlight use <SPC> s c
• helm-swoop bindings are now <SPC> s s, <SPC> s S and <SPC> s C-s.
• don't pair apostrophe in markdown mode (thanks to trishume)
• use web-mode for html files (thanks to danielwuz)
• resize window when golden-ratio is enabled via t g
• add face color for evil-search-highlight-persist in solarized themes
• contribution guidelines have been updated

Do not forget to update the sub modules when you upgrade