Issue317: Introducing Multiple Locale Support

[GarreauArthur]

Partially closes #317

This branch introduces the following new formats (already in use in moment.js):

• LT
• LTS
• L
• LL
• LLL
• LLLL

These tokens define shortcuts to usual, local specific, formats. Example:

dayjs().format('LL');   // August 29, 2018

It works for english, french and spanish. To add a new language, we just need to add the following object into the corresponding locale file. Example (src/locale/fr.js):

  longDateFormat: {
    LT: 'HH:mm',
    LTS: 'HH:mm:ss',
    L: 'DD/MM/YYYY',
    LL: 'D MMMM YYYY',
    LLL: 'D MMMM YYYY HH:mm',
    LLLL: 'dddd D MMMM YYYY HH:mm'
  }

[codecov-io]

Codecov Report

Merging #318 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #318   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          32     32           
  Lines         386    395    +9     
  Branches       53     54    +1     
=====================================
+ Hits          386    395    +9

Impacted Files	Coverage Δ
src/locale/fr.js	100% <100%> (ø)	⬆️
src/index.js	100% <100%> (ø)	⬆️
src/locale/es.js	100% <100%> (ø)	⬆️
src/constant.js	100% <100%> (ø)	⬆️

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[iamkun]

Thanks. I'm not sure if we should add this logic into our main bundle or not. Wait for discussion.

[limonte]

As a dayjs user, I'd like to have this in the main bundle 👍

[prantlf]

I added this functionality as a plugin in #305.

Differences to this PR:

• Additional formatting tokens introduced as a plugin called LocalisableFormat.
• Included formats of the new tokens for all locales.
• Added documentation.

Plugins bring modularity to Date.js. Varous features can be loaded only by applications, which need it. For example, if an application has a date format in the user configuration, it will not need choosing the format by the user's locale from format aliases in Day.js.

[iamkun]

Thanks @prantlf and @GarreauArthur. I tend to agree with prantlf's PR of adding this functionality as a plugin.

[GarreauArthur]

I am down for @prantlf's plugin. 😄

[prantlf]

Thank you all! :-) I'm looking forward to getting it merged :-)

I would like to replace Moment.js with Day.js, but formatting according to the the user's locale (PR #305) and incorrect localisability of relative times (PR #304) do not allow it yet.

The application, which I am working on, runs in two modes:

• The user chooses the format provided by their native locale. Web browser OS, whatever they do. The user wants to have the web application consistent with the rest of their environment.
• The user chooses the format (very) explicitly. Like "DD/MM/YYYY HH:mm:ss". The user wants the web application to be consistent with the company standard, which other intranet web pages adhere to.

[iamkun]

#305 plugin