Fix api reference docs

[typhoonzero]

Some document polish work.

[reyoung]

I just polish templatedoc() a little bit to generate better documentation. Make it support inline math and correct the google style comments. See #11308.

Also, as discussed with @shanyi15 yesterday, we decided to use a new repo to manage documentation of fluid for several reasons.

1. We need cross hyperlink between API-reference, API-Guide and User story. In Paddle, we separate API, use case into many sphinx projects( around 10 sphinx projects before... T_T ). They cannot be cross-link well.
2. It is hard to build documentation before. Use cmake to drive sphinx-build is tricky. We can separate them into two projects. It is easy to complete i18n later if we use a standard sphinx project structure.

Current, this repo(https://github.com/reyoung/FluidDoc) is in very early stage and flux. However, it is very simple to build a documentation site follow the readme.

You can install your developing version of paddle, and make html. The documentation will be generated well at build/html directory.

The develop branch of this documentation will be generated to readthedocs.org. http://fluiddoc.readthedocs.io/zh_CN/develop/ . It uses our latest release paddle to generate.

[typhoonzero]

@reyoung Thanks for polishing templatedoc, I was looking into the format problem using local compiled server. Glad that you already make a fix.

[typhoonzero]

This line is intended to fix build on macos

[skylarch]

@typhoonzero

• API Definition：
• Function Description
	○ Function Description：缺标题：chunk_eval、sequence_conv、matmul、row_conv；标题格式除介词外首字母大写，无句号：smooth_l1、lrn；删除标题：cross_entropy、square_error_cost、conv2d_transpose、sequence_expand、2_normalize、sequence_reshape、transpose、multiplex、softmax_with_cross_entropy、one_hot、lod_reset
	○ Formula：linear_chain_crf、crf_decoding、cos_sim、dropout、chunk_eval、sequence_conv、sequence_pool、pool2d、sequence_expand、reduce_sum 、reduce_mean、reduce_max、reduce_min、reduce_prod、split、matmul、edit_distance、warpctc、sequence_reshape、transpose、smooth_l1、one_hot、autoincreased_step_counter、reshape、lod_reset、pad（如果有API没有formula，就可不做修改）
	○ Symbols' Descriptions if necessary：改为列表格式，和之前的保持一致: dynamic_lstm、dynamic_gru、gru_unit、multiplex、label_smooth
	○ References if necessary：
• Args Description
	○ [Arg’s Name]：
	○ [(Data Type, Default Value（无需重复）)]
	○ [Description]：
• Returns
	○ [Name][Shape]：
	○ Tuple逐个介绍各参数：
• Raises
	○ [Exception Type][Condition]：
• Note分条列出：
• Examples：linear_chain_crf、crf_decoding、chunk_eval、sequence_conv、pool2d、batch_norm、beam_search_decode、beam_search

还未注释：sequence_softmax、softmax

[skylarch]

request changes as commented

[skylarch]

@typhoonzero
现在@reyoung 老师可能对注释内容有新的建议，API注释标准暂时待定，之前的comment可以先不做修改。

[skylarch]

@typhoonzero
comment已根据最新标准更新，可以开始做修改。

[typhoonzero]

@skylarch Added screen shot of the document preview.

[skylarch]

@typhoonzero

chunk_eval:
缺标题；
缺examples；
“see below for details"指的是哪一部分呢？这些可能是有问题的${chunk_scheme_comment}，${num_chunk_types_comment}，${excluded_chunk_types_comment}

iou_similarity
标题格式除介词外首字母大写，无句号，加粗

ctc_greedy_decoder
截图不全

ListenAndServ
标题格式除介词外首字母大写，无句号，加粗
缺return

autoincreased_step_counter
缺例子

conv2d_transpose
标题格式除介词外首字母大写，无句号，加粗
截图不全

roi_pool
标题格式除介词外首字母大写，无句号，加粗
例子或截图不全

crf_decoding
例子

scale
例子

cos_sim
标题格式除介词外首字母大写，无句号，加粗
例子

[reyoung]

[reyoung]

Excellent

[reyoung]

Cool