Performance Improvement and possibility to add a start date to task

[morstin]

• better performance if re-reading files:
  When updating the TodoReview window only changed files are read newly - this makes the work flow very nice as you can change your todos and quickly update your TodoReview window even if you have thousands of files in your project

• adding the possibiliy to specify a start date with @start(yyyy-mm-dd) in the TODO item
  results will then be grouped into: (1) Now, (2) Important, (3) Someday and (4) Future by following rules

(1) Now: start-date of today or older
(2) Important: above defined priority - default < 80
(3) Someday: all items with below defined priority - default >= 80
(4) Future: start-date in the future

This gives a system similar to what is described by https://www.michaellinenberger.com/mywn-book.html
http://blog.clearcontext.com/WindowsLiveWriter/conveyorIdeal2.png

[jfcherng]

For people who may interest, I have my performance improvement on my fork too.

• perf: great speed up by merging regexes into one (this one results in a dramatic performance improvement)
• perf: use set() to gain some speed up

[dg-pb]

For people who may interest, I have my performance improvement on my fork too.

• perf: great speed up by merging regexes into one (this one results in a dramatic performance improvement)
• perf: use set() to gain some speed up

If using set, seen_paths is not needed anymore I believe.