Avoid requiring match is certain circumstances

Closes #115
company-backends: add better introduction

#115
company-capf.el: Don't ignore things like semantic-capf
Release 0.8.1
company-frontends-set: never modify VALUE destructively

Fixes #148
Fix popup when prefix is split by line continuation

#149
company-pseudo-tooltip-frontend: Small rewrite
company-pseudo-tooltip-guard: Invalidate after crossing line continuation
company-pseudo-tooltip-guard: Stabilize when the popup is displayed up
+1 char, -1 line
Deprecate setting company-idle-delay to t
company-sort-by-occurrence: allow customizing the weighing logic

Closes #152
company-sort-by-occurrence: continue search after predicate fails
company-capf: get rid of caching last capf-data

It didn't work well enough.

Fixes #153.