学习backtrader框架（第一回）

backtrader的设计很新颖。

两个基础

1. lines

Data Feeds, Indicators and Strategies have lines.
A line is a succession of points that when joined together form this line. When talking about the markets, a Data Feed has usually the following set of points per day:
Open, High, Low, Close, Volume, OpenInterest
The series of “Open”s along time is a Line. And therefore a Data Feed has usually 6 lines.
If we also consider “DateTime” (which is the actual reference for a single point), we could count 7 lines.

backtraders 自己创造了个“线”的概念，数据是由 Open, High, Low, Close, Volume, OpenInterest 这6个元素构成，每个元素的序列就是一条“线”

DataFeeds, Indicators, Strategies 都有“线”。

2. index 0

backtrader的索引和python不同，索引0指向当前的数值，-1是倒数第二个数值。
之所以这样做，是方便在时间序列里获取当前的数值。我认为

其他方面

1. system clock (backtrader立时)
   无论是回测或者